The Republican lawyer asks about Ukrainian Minister Arsen Avakov, who criticised Trump online when he was a candidate for US president.

"He said some real nasty things" about Trump, says Castor.

"Well, sometimes that happens on social media," says Yovanovitch, triggering laughter in the hearing room. Moments ago Trump tweeted criticism of her during the televised hearing.

"I am shocked that social media would be the source of negative comments," jokes the Republican lawyer, in response.

Need to catch up with all things Trump impeachment? We’ve made it easy for you.

SIMPLE GUIDE: If you want a basic take on what's going on, this one's for you

GO DEEPER: Here's a 100, 300 and 800-word summary of the story

WHAT'S IMPEACHMENT? It's a political process to remove a president - video guide

VIEW FROM TRUMP COUNTRY: Hear from residents of Pennsylvania

ON THE DOORSTEP: A newly elected Democrat sells impeachment to voters

Image source, Getty Images

"Is Hunter Biden a genius?" asks Republican lawyer Steve Castor.

Republicans wanted the son of ex-vice president Joe Biden to testify to the committee but the Democrats refused.

Hunter Biden worked for Ukrainian energy firm which has been investigated for corruption. The Republicans suspect he was hired because of his powerful father.

So what do we know about the corruption claims against the Bidens?

Some on social media have condemned Yovanovitch's treament by Republicans (and the president) during the hearing - saying the language has been "jarring".

Former Secretary of State Hillary Clinton has also weighed in on what Democrats are calling witness intimidation by the president.

Image source, Chip Somodevilla/Getty Images

The man questioning Yovanovitch right now on behalf of Republicans is Steve Castor.

He is a congressional staff lawyer who played a key role in several significant Obama-era investigations - including into 2012 attack against the US diplomatic mission in Benghazi, Libya.

Image source, Sarah Silbiger/Getty Images

The official who allegedly overheard Trump inquire into the status of "investigations" in Ukraine - shortly after his July call with the Ukrainian president - has been called to appear before lawmakers in a closed-door session on Friday.

Bill Taylor - acting ambassador to Ukraine - testified on Wednesday that a staff member heard Trump refer to probes in Ukraine and mention his interest in the Bidens.

"The member of my staff could hear President Trump on the phone, asking Ambassador Sondland about 'the investigations,'" Taylor said Wednesday.

CBS News has named David Holmes as the official. Holmes is a counselor at the US embassy in Kyiv.

Read more on Taylor's testimony here.

Image source, SAUL LOEB/AFP via Getty Images

"Ambassador Taylor is a good pick?" says Castor, asking about William Taylor, the diplomat chosen by Trump as Yovanovitch's temporary replacement in Kyiv.

She agrees, calling him a man of "integrity". Taylor testified on Wednesday that top Trump aides led a smear campaign against US diplomats in Ukraine.

Republicans say Trump has the right to hire and fire ambassadors as he pleases.

"This hearing room has turned into a television studio," Republican counsel Steve Castor begins.

He then clarifies that Yovanovitch's tenure in Ukraine was expected to end in 2019 and confirms that she's still employed by the state department.

She also now has a position at Georgetown University in Washington DC, he points out.

"I'm very grateful to be in that position after what happened," Yovanovitch answers.

Republican Nunes accuses Schiff of "gagging the young woman from New York" after the Democratic chairman refuses to allow Congresswoman Elise Stefanik to speak on Nunes' behalf.

"The gentlewoman will suspend," Schiff says, speaking over Stefanik.

Schiff overrules Nunes' request to let her speak, and now Steve Castor, the lawyer for the Republicans on the panel, is asking questions.

Image source, Bill Clark/CQ-Roll Call, Inc via Getty Images

Republican Chairman Devin Nunes now has 45 minutes of questions.

He starts by issuing a "congratulations" to Yovanovitch on her "performance today".

The hearing resumes as lawmakers return from their recess.

After the first public hearings, we spoke to a Democrat and a Republican to get their reactions. Here's what they had to say.

Image source, Sergei Chuzavkov/SOPA Images/LightRocket via Getty Images

Ukrainian President Volodymyr Zelensky told reporters in October there had been “no blackmail” in the call with Donald Trump that led to this impeachment probe.

The purpose of the conversation, he said, was to arrange a meeting with Trump, and no "conditions" were placed by the Americans.

Zelensky also said he did not believe US-Ukraine relations would be affected by the impeachment inquiry.

Roger Stone, a top adviser to Donald Trump, has been found guilty of charges related to the Trump-Russia probe led by Robert Mueller.

He was found guilty of all seven counts against him, including witness tampering and obstructing the investigation by the House Intelligence Committee, where Yovanovitch is testifying today.

He is facing up to 50 years in prison.

Read the full story here.

Republicans have yet to question Marie Yovanovitch. The panel's top Democrat and Republican each get 45 minutes for questions under committee rules, following by five-minute sessions from the other lawmakers on the panel.

In his opening statement, the panel's top Republican Devin Nunes accused Democrats who lead the panel of creating "day-long TV spectacles instead of solving the problems".

Several Republicans have argued that Democrats have been trying to make Yovanovitch cry. Transcript of her closed-door testimony last month shows she grew emotional while talking about being "threatened" by Trump.

Image source, Fox News

The Washington Post's Dan Zak is following coverage on Fox News, Trump's favourite network.

Ken Starr, the prosecutor who led the impeachment of then-President Bill Clinton, told the network that Trump's tweet showed "extraordinarily poor judgment... I think this was quite injurious."

Presenter Chris Wallace told viewers: "If you were not moved by the testimony of Marie Yovanovitch, you don’t have a pulse... It seems to me that this has been very powerful testimony this morning."

Image source, Google Trends

As Marie Yovanovitch began her testimony and Trump live-tweeted his reactions, Google searches for the dismissed diplomat spiked in the US.

Tara McKelvey
BBC News, Pennsylvania

Image source, Tara Mckelvey

The impeachment inquiry has taken over Washington in recent weeks. But beyond the Beltway, does anyone care?

As the BBC's Tara Mckelvey writes from Pennsylvania, voters in the Trump heartlands are deeply suspicious of Democratic lawmakers.

Lynn Gramling, a businesswoman, watched the hearing on Wednesday. When Adam Schiff, the Democratic chairman of the House intelligence committee, spoke, she made a face. "Shifty Schiff", she said, using the president's nickname for the lawmaker.

Pennsylvania is a key state for 2020. Trump lost the national vote by two points in 2016. But he won the presidency thanks to victories in Pennsylvania, Michigan and other states that are rich in electoral votes.

Read the full story here.

President Donald Trump is in the middle of an impeachment inquiry.

The BBC's Ritu Prasad, Laura Trevelyan and Chris Buckler break down the key points.

Anthony Zurcher
BBC North America reporter

Image source, Matt Sullivan/Getty Images

Donald Trump has boasted that his conduct while in office – blunt language and shoot-from-the-hip tweeting - is "modern-day presidential".

If so, welcome to a modern-day presidential impeachment hearing.

Just over an hour into Marie Yovanovitch’s testimony, Mr Trump launched the kind of Twitter fusillade that has become a regular part of his political repertoire. He questioned the ambassador’s competence, noted that the Ukrainian president spoke unfavourably about her and pointing out that he has the right to fire diplomats at will.

What makes the moment historic is that Committee Chair Adam Schiff gave Yovanovitch a chance to refute the president’s tweet almost in real time.

Democrats are already characterising the president’s behaviour as witness intimidation – and the latest attack by the president against one of his own government employees.

Republicans, whose reported strategy was to avoid directly impugning the reputation of a long-serving, respected diplomat, will once again find a president who has changed the rules of engagement on the fly.

On Wednesday, the White House said the president was not watching the impeachment hearings. On day two, the president is fully engaged.

Mr Trump may not be in the hearing room, but his presence is being felt.