Shaimaa Khalil
reporting from Seoul

Outside the compound, two sets of chants are competing against each other.

Yoon opponents are yelling "arrest him", while his supporters are shouting the suspended president's name.

A huge cheer erupted on the anti-Yoon side when it was announced that the police and investigators have made it inside the presidential compound, having pushed through blockades made from buses that had been set up by the presidential security staff.

But the political crisis South Korea is also pitting two branches of executive power against each other: law enforcement officers, armed with a legal arrest warrant that they're trying to execute, and presidential security staff, who say they are duty bound to protect the suspended president.

Both say they're following orders and the rule of law, as the stand off continues.

Earlier, we reported that local media said Kim Sung-hoon, who is the acting head of the Presidential Security Service, had been arrested for blocking the execution of the warrant.

Korean media are now reporting, however, that Kim has not been arrested.

The situation remains fluid, and we will continue to bring you the latest updates.

Protestors have been a regular sight here for the past few weeks, and this morning huge crowds are out again - anxiously watching to see how investigators fare in their second attempt to arrest Yoon.

Investigators entered the presidential residence compound using ladders, Yonhap reports.

They were blocked earlier by ruling party lawmakers and Yoon's lawyers at the entrance, as well as a barricade of vehicles set up by Yoon's security service. But some investigators reportedly managed to access the compound through a nearby hiking trail.

They have since reached the president's house, and are inside, authorities have confirmed.

Rachel Lee
reporting from Seoul

As news that investigators are advancing inside the compound spreads to the crowd outside, Yoon's supporters are growing increasingly angry and upset. One woman starts crying.

But Hwang Kyo-ahn - the acting president the last time South Korea impeached a leader in 2016 - is here rallying the protestors, urging them not to give up.

Hwang is saying there is still time to save the president and it's not the end.

Members of the crowd are yelling, saying it is illegal for the police to enter the residence. Yoon's lawyers have been claiming the arrest warrant is invalid. Others are aggressively confronting the police to express their objections to the arrest.

We reported that Yoon's side has been reportedly negotiating with investigators about the possibility of voluntarily appearing in front of the Corruption Investigation Office (CIO).

CIO has recently revealed in a news briefing that they won't accept this possibility, and they are still "coordinating" the execution of the arrest warrant.

Investigators say they have entered Yoon's residence.

The door of the residence is open, with staff seen walking in and out. Local media is reporting that Yoon may walk out of his residence soon.

Officers began arriving at the presidential residence around 4:20 local time (19:20 GMT) and the last five hours have been slow-going for them.

They were met by crowds - both in support of Yoon, and in support of the investigators trying to arrest him - which have been a staple at the scene since the embattled president holed himself up there in December.

A force of at least 1,000 police officers have been trying to gain access to the compound from multiple entrances, and a short time ago got through the first few barriers on their way to the president's door.

It's worth remembering that they got about this far during the last arrest attempt on January 3 too. That stand off went on for six hours until police retreated, saying the situation was "impossible" and citing concerns for their safety.

But investigators have successfully made one arrest already today: Kim Sung-hoon, the acting head of the Presidential Security Service (PSS), the team which obstructed the last bid to detain Yoon.

Yoon's lawyers are in negotiations with the CIO regarding the possibility of "voluntarily appearing in front of the CIO," according to Seok Dong-hyun, a lawyer and close associate of Yoon.

“As there have been reports of citizens getting injured outside the residence, and a potential clash between the police and security staff could cause further issues, I heard the lawyers had no choice but to negotiate with the CIO about this,” he said in a post on Facebook.

Kim Sung-hoon, who is the acting head of the Presidential Security Service, has been arrested, according to local media reports.

Since investigators' last attempt to arrest Yoon was foiled by the PSS, Kim defied multiple orders from the police to be questioned on charges of obstruction. The PSS has also been obstructing today's arrest attempt.

Police have now broken through a third blockade at the presidential residence, Yonhap news reports.

Members of Yoon's security detail have set up barricades at the entry, but also at several points within the compound.

Leehyun Choi and Rachel Lee
reporting from Seoul

It's just gone 8:30 in Seoul, and the sun has risen but it's still a freezing -6C in the South Korean capital.

That hasn't deterred the crowds - of both Yoon supporters and critics - who have gathered.

Anti-Yoon protesters are eagerly waiting for the news of an arrest, saying "Finish it ASAP, before commute hours." We've also seen them cheering on police as more groups of officers headed towards the main gate.

Yoon's backers have chanting and making speeches too, waving flags and even placing flower wreaths - usually seen at weddings or celebrations - at the scene, which express words of support for the embattled leader.

At the moment pro-Yoon supporters are gathering in much larger numbers than those who oppose him.

This morning's events are the culmination of almost six weeks of political chaos in South Korea.

This is totally uncharted territory for the country - the first time a sitting president has ever faced arrest. Here's a recap of how we ended up here.

On 3 December Yoon shocked the world by declaring martial law in a late-night televised address, only to back down when lawmakers voted to defeat the measure hours later.

Outcry from all sides of politics was swift and as more details emerged, a second bid by lawmakers to impeach the president - stripping him of his powers pending a court trial - passed on 14 December.

At the same time, police began investigating Yoon and his allies for insurrection.

But Yoon has refused to cooperate with the authorities, ignoring every request to come in for questioning and even so far refusing to turn up at his own impeachment trial which was due to begin yesterday.

And so investigators say they have no other option but to arrest him, and have obtained legal court warrants to do so.

But Yoon - who is supposed to be essentially powerless after parliament voted to remove him from office - used his security teams to thwart their first arrest attempt earlier this month and is trying to do it again today, raising serious and uncomfortable questions about who is in charge here.

We are now into the third hour of the second attempt by the police and investigators to arrest Yoon.

The BBC's Shaimaa Khalil shows us the scene outside the embattled president's residence.

We are now seeing local media reports that police have broken through a second blockade which was made up of buses.

Police have just broken through the first line of people aiming to stop the arrest at the presidential palace.

Live video from the scene shows them moving inside towards a second blockade.

Police say they are executing an arrest warrant against Kim Sung-hoon, who is the acting head of the Presidential Security Service (PSS), as well as Lee Kwang-woo, who is the head of the bodyguard division, according to a report from Yonhap agency.

As a reminder, the PSS has been trying to prevent police forces and investigators from entering President Yoon's residence.

We've been hearing that there have been physical clashes between police and protestors outside the presidential palace, and authorities have confirmed one person has been injured, according to local media.

Fire and emergency authorities have transported that person away for a health check.

Image source, Getty Images

We've seen a statement from acting President Choi Sang-mok, who says conflict between state institutions is unacceptable and would result in harm to the public's trust.

He is referring to the stand off between investigators attempting to arrest Yoon and his Presidential Security Service (PSS).

Choi says the execution of the arrest warrant for President Yoon has commenced, and describes it as a critical moment for maintaining order and the rule of law.

He urges all parties to act with careful judgement and responsible behaviour, adding that people who violate the law will be held accountable.

Investigators' efforts to arrest Yoon follows a failed attempt at the start of this month, where officers found themselves in a dramatic six-hour standoff withsecurity.

Officers involved found themselves helplessly outnumbered - first by the large number of pro-Yoon supporters who had gathered outside his residence before sunrise, and then by a human wall of security staff inside the property.

Police were trying to carry out an arrest warrant issued on 31 December after Yoon ignored three summonses for him to appear for questioning.

The politician is under investigation for abusing his power and inciting an insurrection when he tried to impose martial law in early December.