It's mid-morning in the eastern state of Odisha, and a sweltering 33C (91.4F) for the waiting voters - not that it's putting them off.

In a country of India's size, there's room for huge variation in conditions. BBC weather predicts warm, scattered storms rolling in over the north-west - and what looks like rain over Kerala.

As long as this election might seem - it's going to take 39 days - it's still not the longest one India has actually held.

That honour goes to India's first election, which lasted nearly three months - from 25 October 1951 to 21 February 1952.

Here's a photo of people queuing up to vote in the eastern city of Calcutta in January 1952.

Image source, Getty Images

Between 1962 and 1989, elections would take between four and 10 days.

The four-day elections in 1980 were the country's shortest ever. Indira Gandhi, pictured below, won that election to become prime minister for the third time.

Image source, Getty Images

If the state of Uttar Pradesh were a separate country, it would be the fifth-largest by population in the world after China, India, the United States and Indonesia.

Commonly called UP, this is India's most populous state. It has 222 million people.

People are voting today for eight constituencies in Uttar Pradesh, out of a total of 80.

UP sends the largest number of MPs - 80 - to India's parliament. It’s often said that the party that wins the state rules the country.

Today, 96 candidates are on the ballot across 16,633 polling booths.

The state played a key role in the governing BJP party's 2014 election win. Of the 282 seats the party of Prime Minister Narendra Modi won, 71 were from UP.

You can't escape it. Every Indian election sees a flood of images featuring smiling voters holding up fingers.

Case in point:

There's a reason for this:

Once you've cast your vote inside a polling booth, an election official marks your index finger with indelible ink.

This is primarily to prevent people from turning up multiple times and casting votes using the names of other people on the voting list. (This has happened more often than you might think...)

It's also immediate visual proof that you've fulfilled your duties as a responsible citizen and voted.

Many social media campaigns urging people to take "voter selfies" have caught on in recent years, all showing them proudly displaying their inked fingers.

If you're just joining us, here's what's happened so far:

The world's largest democratic exercise kicked off at around 07:00 local time. Some 142 million people are voting today in 18 states and two union territories, and they will elect representatives for 91 parliamentary seats.

But it's just the first of what will be seven days - or phases - of voting.

So far, things appear to be going according to plan - even in sensitive areas like Indian-administered Kashmir, where people are voting amid tight security.

Elsewhere in India, people have been queuing up to cast their ballots.

Image source, Getty Images

Voters of all ages and from all walks of life - from tribal women to nuns - have been turning up to participate.

Image source, Getty Images

Image source, Getty Images

Former Indian army chief Gen VK Singh is the BJP candidate from Ghaziabad in the bellwether state of Uttar Pradesh.

He is the junior minister for external affairs in the current government.

General Singh is being challenged by Dolly Sharma, an entrepreneur turned politician running for the Congress Party, and Suresh Bansal, who represents an alliance of strong regional parties.

But he will not be easy to beat. In the last election, he trounced his rival - former Bollywood actor and state Congress party chief Raj Babbar - by more than half a million votes.

Soutik Biswas
India Correspondent

Indian women are voting in large numbers. So much so, that more women are likely to vote than men this time around, the first time ever in a general election.

The vote gender gap has already shrunk - in 2014, the turnout of women was 65.3% against 67.1% for men.

In more than two dozen local elections between 2012 and 2018, the turnout of women was higher than men in two-thirds of the states.

Political parties have begun treating women as a constituency and offering them more sops: education loans, free cooking gas cylinders and cycles for girls.

Millions of votes will be cast via electronic voting machines in the weeks to come. First used in India in 1982, they've been taken to far-flung districts by helicopter and even by camel!

The crucial boxes are powered by batteries and look like briefcases. This time round, a receipt will be printed every time a ballot is cast, and stored in a sealed box.

In the past, losing parties have often declared the machines were hacked - but India's Election Commission says there's no evidence they've ever been interfered with.

Our correspondent Soutik Biswas spoke to cyber experts to ask: Are fears of a mass hack credible?

Image source, Reuters

What does this candidate have against voting machines?

"It's totally bogus...completely wrong," he says, while smashing it to the ground a second time.

As many as 185 candidates are competing to represent a single constituency - Nizamabad - in the southern state of Telangana.

And it's confusing voters!

Nizamabad is the only constituency to use 12 voting machines - that's how many it took to log the names of every candidate.

Almost all of them are farmers - and they are contesting as independents as a form of protest. They say their demand for higher crop prices has been repeatedly ignored.

India's deepening agrarian crisis is a crucial election issue - farm incomes have stagnated because of a crop glut and declining commodity prices, leaving farmers in debt and angry.

When does each state go to the polls? Here's a rundown.

Voting will be held on 11 April, 18 April, 23 April, 29 April, 6 May, 12 May and 19 May.

Polling in some states, such as Tamil Nadu and Andhra Pradesh, happens in a single day. But other states, such as Uttar Pradesh, will hold polls in several phases.

And the big results day? That's 23 May.

Voting has begun on a peaceful note in Baramulla in Indian-administered Kashmir, though amid tight security.

Baramulla is a particularly sensitive area. The Line of Control (LoC) - the de facto border between India and Pakistan in Kashmir - runs through all three districts of this constituency.

It frequently witnesses cross-border shelling and firing, especially when tensions between India and Pakistan escalate.

BBC Urdu's Riyaz Masroor who is in Handwara district, a major town near the LoC, says schools and offices are shut because militants have called for a poll boycott.

However, he says that people are still lining up to vote.

"It's still early but I can see a lot of men and women," he said.

We are talking to some of the people gathered outside polling booths from across the country.

Here is what some of them have to say:

In Uttarakhand, almost 10% of the state's 7.8 million voters cast their ballots in the first hour, a poll officer told the Hindustan Times. Some 52 candidates are standing there in five constituencies.

The BJP currently holds all five of the state's parliamentary seats, and the Congress Party (which held all five before the last election in 2014) - is the main opposition fighting to reclaim them.

Jobs are a hugely important issue this election.

Unemployment has risen, and Prime Minister Narendra Modi's government has been accused of witholding reports that show uncomfortable jobs data.

Read more: India job data spells trouble for Narendra Modi

The BBC's correspondents are spread out across India to report on the voting. Here is what they are seeing so far:

Chandrababu Naidu, the chief minister of Andhra Pradesh, and his family have cast their votes in Amravati - the new capital of Andhra Pradesh.

The southern state is one of those that will finish voting today - but a number of polling booths are reportedly seeing delays due to malfunctioning Electronic Voting Machines (EVMs).

The chief minister has previously demanded a return to paper ballots, calling the machines a "threat to democracy".

Andhra Pradesh could be a crucial ally in any federal coalition.

Three regional parties are competing for its 25 parliamentary seats. Mr Naidu has been campaigning heavily to retain power - he is up against Jagan Mohan Reddy, head of the YSR Congress and Pawan Kalyan, a southern film actor-turned politician, who recently founded the Jana Sena Party.

The stakes are especially high since Andhra Pradesh is also voting to elect its state legislature. Mr Naidu's son, Lokesh, also seen in the photo above, is a candidate in the state polls.

India's elderly certainly take their duty as voters seriously. Here are some of the country's oldest citizens making sure they exercise their franchise.

Image source, Getty Images

Image source, Getty Images

Image source, Getty Images

Suspected Maoists detonated an IED bomb near a polling booth in the Narayanpur constituency at around 0400, police have confirmed to the BBC.

No injuries were reported, and our correspondent Salman Ravi says that voting is still taking place there.

The mineral-rich state has witnessed an armed conflict for more than three decades and attacks by Maoist rebels on security forces are common. A state lawmaker was killed in a suspected rebel attack on Tuesday.

Maoists are opposed to the concept of the Indian state and want to force people into boycotting the vote, our correspondent says.

This update from our correspondent Soutik Biswas:

Voters are slowly beginning to stream out of their homes in Cooch Behar, a town in West Bengal close to the border with Bangladesh. Shops and offices are shut. Traffic is sparse.

More than 1.8 million voters are eligible to cast their ballots from this seat today. The contest is between the ruling, regional TMC and the BJP - and it is expected to be keenly fought.

Rabindranath Ghosh, a powerful local TMC leader and a minister in the West Bengal government, is travelling in the constituency to find out how the ballot is going.

He tells reporters that some of the EVM machines are not working because of a "conspiracy by the BJP." None of this can be verified.