Authorities are trying to understand what led a 22-year-old man to set off a bomb at Manchester Arena on Monday night local time.

At least 22 people, including children, were killed and 59 wounded in the attack at a concert by singer Ariana Grande.

The suspected attacker was named as Salman Abedi, aged 22.

Two US officials who have been in contact with British authorities said he was believed to have travelled to Manchester from London by train.

Abedi was born in Manchester - his parents fled to the UK from Libya to escape the Gaddafi regime.

Senior reporter for radio station LBC, Vincent McAviney told Mike Hosking ISIS has claimed responsibility for the attack.

"It is still unclear yet what the specific motive for it was. Whether or not this person was in direct contact with the so-called Islamic State or if he was acting on his own and they are now just simple claiming credit," he said.

Thousands of people turned up to honour the dead at a vigil held at Albert Square in Manchester. 

Mr McAviney told Mike Hosking politicians, religious leaders and emergency services were also present. 

"There was a strong spirit of unity in the crowd. People of all ages, faiths, colours, creeds [that] I've been talking to here, coming together saying they are shocked and appalled by this, saying it doesn't represent one or any religion," he said.

LISTEN ABOVE TO VINCENT MCAVINEY SPEAK WITH MIKE HOSKING