A man believed to be Sudanese has been arrested on suspicion of attempted murder after a "brutal" knife attack in Belfast, police have said.

The man, in his 30s, remains in custody after the incident in north Belfast at about 22:30 BST on Monday.

Video circulating online shows several people, including one wielding a hurling stick, confronting the apparent attacker until the police arrived.

A man injured in the attack, aged in his 40s, is in hospital where his condition is described as serious.

An initial statement from the PSNI on Tuesday morning said police believed the attacker was Somali, but have since confirmed he is Sudanese, describing it as a "fast-time investigation".

A spokesperson said police are "aware of inaccurate online posts regarding the victim's condition", but confirmed he remains in a serious condition.

Prime Minister Sir Keir Starmer called the incident "sickening", adding that he will have "absolutely no tolerance for abhorrent scenes of violence like this on our streets".

"The horrific attack in Belfast last night is sickening," the prime minister said.

"My thoughts are first and foremost with the victim, and I thank the first responders, including members of the public who intervened."

The Northern Ireland secretary said the attack was "deeply shocking".

"I would like to thank the individuals who showed extraordinary bravery in coming to his aid," said Hilary Benn.

Benn appealed for calm and warned of the impact of violent street disorder in Ballymena in County Antrim and Belfast in recent years.

"We all have a responsibility to urge calm while the police do their job, so that the perpetrator of this horrific attack faces the full force of the law," he said.

He was speaking in the House of Commons in response to an urgent question from the leader of the Democratic Unionist Party (DUP).

Gavin Robinson described the stabbing as "chilling" and "medieval" as he praised members of the public who intervened.

He told MPs the incident "will have profound implications for community cohesion in this country".

Robinson asked the government to recognise "uncontrolled immigration needs to end".

Calling for calm, he said that "community cohesion lies on the precipice".

'Shockwaves through community'

Emergency services were called to the Kinnaird Avenue area in north Belfast on Monday night.

The victim sustained significant injuries to his face, neck, and back.

Police Service of Northern Ireland (PSNI) Assistant Chief Constable Ryan Henderson said "a critical incident" has been declared and police have begun an investigation to establish a motive.

"This brutal attack will have sent shockwaves through the community, causing real concern.

"I want to reassure the local community that we are treating this attack with the utmost seriousness.

"Our investigation is continuing at pace."

Henderson said police were on the scene within minutes and acknowledged the members of the public "who strived to save the man from further attack".

He said they demonstrated "bravery and community spirit".

He asked that people do not share footage of the attack.

'I was just absolutely petrified'

A resident told BBC News NI how she was in her home when her partner heard screaming outside.

She said others, including children, had begun to gather in the street and described how some people tried to intervene.

The woman said she had "never seen anything like it".

"The police came and I kept my kids in the house; I was just absolutely petrified.

"I feel frightened."

In a joint statement, Northern Ireland's five main political parties are "united" in their condemnation of the "horrific incident".

It was signed by Sinn Féin's Michelle O'Neill, the Alliance Party's Naomi Long, Jon Burrows from the UUP, the DUP's Gavin Robinson, and Claire Hanna from the SDLP.

"There is no place in our society for this kind of brutality," they said, adding that their thoughts are with the victim, his family, all those who witnessed the attack, "as well as those brave members of the public who intervened".

Party leaders acknowledged "the distress and fear this incident will cause", but urged "people not to share the deeply disturbing images or videos".

Backing the PSNI and their ongoing investigations, they urged anyone with information or relevant footage to contact police.

"We are committed to ensuring that violence and hatred in any form will not be allowed to divide our communities.

"We call for calm and for space to allow justice to take its course."

First Minister Michelle O'Neill described the attack as "harrowing".

"I also want to recognise the bravery of members of the local community who put their own safety at risk in an effort to stop this vicious attack."

Northern Ireland's Justice Minister, Naomi Long, said "there is no place for this kind of horrific violence in our community", adding this was a time to "remain calm and lawful and allow the police to do their job".

Deputy First Minister Emma Little-Pengelly said people across Northern Ireland were "sickened and appalled" by what had happened.

"I know emotions are running high - there is anger and concern, but I do urge everyone to remain calm to allow the police to carry out their investigation and allow people to establish the full facts."

Leader of the Conservative Party, Kemi Badenoch, said she was "absolutely horrified" by the attack.

"I think a lot of people will start wondering yet again, is this someone who should not have been in our country? Have there been failings around our borders?

"I would urge the police to bring the facts out as quickly as possible so that we can get some clarity," she said.

Reform Party leader Nigel Farage described the attack as "horrific".

"The authorities must reveal the identity and status of the attacker immediately.

"The public are entitled to the truth."

Rupert Lowe, leader of Restore Britain, has told people to "demand answers" around the attack.

Jim Allister, leader of the Traditional Unionist Voice (TUV), said the "only bright spot in this dark orgy of violence" was the group of locals who stopped the attack.

"Cool heads, of course, are needed, but the police and the government must be shown to be effective."

Paul McCusker, an independent councillor in the area, said "one lady said she had to go to hospital herself because of the stress of witnessing such a brutal attack".

He praised the "brave residents" who intervened to stop the attack.

A statement from the North West Migrants Forum said they are "absolutely horrified" by the news and recognise that people will be "traumatised" by what they witnessed.

It added: "Obviously, attacks like this do not make our job any easier, and we understand completely that many people will feel frightened, angry, and in want of answers.

"Our members are also frightened. Good, decent, honest men and women fretting this morning about what last night's attack will mean for them."