The 22-year-old British-born man responsible for detonating an improvised explosive device after a concert at Manchester Arena, killing 22 people and injuring 59 more, was reportedly a university dropout who had recently become radicalised.

Police have identified Salman Abedi as the suicide bomber behind the attack.

Reports suggest the 22-year-old had recently visited his family’s native country Libya, where it's believed he may have been preparing for Monday’s attack under the guidance of jihadists.

The face of evil: Salman Abedi. (The Sun)

The Times reported the Manchester-born bomber spent three weeks in the war-torn north African nation before the attack on Manchester Arena, in which he was killed.

A friend told the paper: "He went to Libya three weeks ago and came back recently, like days ago."

Islamic State, who claimed responsibility for the attack, and al-Qaeda have a presence in Libya.

Abedi reportedly worshipped at the suburban Didsbury Mosque, a former Methodist chapel, in a leafy suburb where his father was well-known and sometimes performed the call to prayer.

Heavily-armed police earlier conducted a raid at Abedi's home in Fallowfield, performing a controlled explosion to gain entry.

British Prime Minister Theresa May raised the UK terror threat level to 'critical' following the deadly bombing.

"This means their (Joint Terrorism Analysis Centre) assessment is not only that an attack remains highly likely, but that a further attack may be imminent," Ms May said after the second Cobra meeting between high-ranking officials today.

Abedi reportedly grew up in the Whalley Range area in southwest Manchester.

Neighbours told AFP they recalled an abrasive, tall, skinny young man who was little known in the neighbourhood.

He is thought to have lived at a number of addresses in the area, including one in Wilbraham Road, where plain-clothes police made an arrest of a 23-year-old man, believed to be the bomber’s brother, on Tuesday.

Abedi reportedly previously lived with his mother, Samia Tabbal, father Ramadan Abedi and a brother, Ismail Abedi, who was born in Westminster in 1993.

He studied business and management at Salford University two or three years ago, a source said, but did not complete his degree.

He did not live in university accommodation, had not been in any trouble at the university, was not on any radar for pastoral or social care and was not known to have participated in any university societies.

His family lived in Manchester for at least 10 years, according to The Telegraph .

Ms May said it was a possibility a "wider group of individuals" was linked to the attack and has increased police presence and armed forces at "key sites" around the region.

"You might also see military personnel deployed at certain events such as concerts and sports matches, helping the police to keep the public safe," she said.

Extra police and armed soldiers have been deployed at key sites around the city, Ms May said.

The youngest victim identified so far is eight-year-old Saffie Roussos, from Lancashire, north-west of Manchester.

Georgina Callander, 18, and John Atkinson, 28, Kelly Brewster, 32, and Alison Howe have also been identified as among the dead.

Eight-year-old Saffie Rose Roussos was killed in the blast.

John Atkinson, 28, has also been named among the victims. (Facebook)

Georgina Callander, who died in the Manchester attack, posted a photo with Grande to social media, (Supplied/Instagram)

Read more: Victims as young as eight identified

A mother who made a heartfelt plea for information about her missing daughter, 15-year-old Olivia Campbell, has since confirmed she was killed in the attack in an emotional Facebook post.

The attack is the deadliest militant assault in Britain since four British Muslims killed 52 people in suicide bombings on London's transport system in July 2005.

Queen Elizabeth II condemned the attack as an "act of barbarity", voicing sympathy for victims and emergency workers.

"The whole nation has been shocked by the death and injury in Manchester," the Queen said in a statement, adding: "I would like to express my admiration for the way the people of Manchester have responded, with humanity and compassion, to this act of barbarity".

It is understood Ariana Grande has cancelled the remainder of her European tour, which was expected to reach London on Wednesday night.

Grande, 23, took to Twitter to declare she was “broken”, and her management team have praised the work of emergency services.

English pop group Take That was due to perform in Liverpool on Tuesday night local time, but postponed their performance.

"Out of respect to all of the people and their families that were affected by the horrific incident last night at The Manchester Arena, we have decided to postpone our show tonight in Liverpool. Our thoughts and prayers are with you all," the band said on Twitter.

Witnesses have continued to share their stories of the carnage, with many saying debris was strewn across the area.

"When we left, down the stairs there was probably early teenagers lying on the floor covered in blood and blood on the walls where they'd been laid, so it was just horrifying," concert-goer Alex Grayson told AFP.

One mother told the BBC she and her husband were at the arena to pick up her children, aged 15 and 17.

"We were stood at the top of the stairs and the glass exploded — it was near to where they were selling the merchandise," Emma Johnson told BBC Radio Manchester.

Police locked down the area following the explosion. (Supplied)

"The whole building shook. There was a blast and then a flash of fire afterwards. There were bodies everywhere."

Video filmed in the arena's auditorium appears to show fans running in panic after hearing the blast.

The arena's foyer connects the 21,000-capacity auditorium with Victoria train and tram station, a major hub on the northern edge of the city centre.

Andy Holey, who was waiting to pick up his daughter and wife from the concert, told the BBC he was blown "about 30 foot" by the blast and saw "carnage everywhere".

He said he struggled to find his wife and daughter and looked at bodies on the ground to try and find them.

Police are treating the blast as a terrorist incident. (Supplied)

"Luckily they weren't there, I managed to find them outside the arena and got them back to the hotel," Mr Holey said.

Both Ms May and Labour rival Jeremy Corbyn have suspended their general election campaigns in the wake of the attack.

Prime Minister Malcolm Turnbull has described the attack as a an " attack on innocence ", while Foreign Minister Julie Bishop said there was "no evidence" Australians were caught up in the "cowardly, callous attack".

Ms Bishop told the TODAY Show she would not recommend travelling to Manchester while the investigation is underway, and pointed to the government's updated Smart Traveller advice for information.

"It's quite evident (the attack) was part of a broader effort. While the police investigation is underway, people need to be cautious and take great care with their travel to the United Kingdom," she said.

Australia's terror threat level remains at probable.

Australians travelling in the UK have been advised to steer clear of Manchester Arena, and expect a heavier police presence across the region.

"In light of the UK's increase to its threat level, we now advise you to exercise a high degree of caution in the United Kingdom," the advice reads.