Two other people killed were earlier confirmed to be 19-year-old students in the city.

Police declared a major incident after the pair were found dead in the street in Ilkeston Road just after 4am.

A witness reported seeing a young man and young woman being stabbed there.

Nottingham attack - follow live updates

Officers were then called to Milton Street, in the city centre, where a driver had tried to run over people in a van. One person is in a critical condition, two others have minor injuries.

The man in his fifties was found dead with knife injuries by a member of the public in nearby Magdala Road.

The University of Nottingham said it was "shocked and devastated" as it revealed two of its students were among the dead.

Police have arrested a 31-year-old man on suspicion of murder and he remains in custody.

Video appears to show him on the ground next to the van as officers detained him.

Photos of the vehicle show small cracks on the windscreen and apparent damage to the bumper.

Chief Constable Kate Meynell said they believe it was stolen from the middle-aged victim and used to drive at members of the public.

Police are working alongside specialist terror officers, but say they are keeping an "open mind" over the motive and are not looking for anyone else.

Read more:
A timeline of how 'major incident' unfolded
Witness describes 'scream' as van hit two people
What we know about the attack so far

Hours after the attacks, at around 12.30pm, there was a "flurry of activity" as armed police cut off Ilkeston Road - where the students were stabbed, said Sky correspondent Becky Johnson.

She said two young women were put in the back of a marked car after officers appeared to enter a commercial property.

Chief Constable Meynell later said a number of searches had been carried out across the city but no further arrests.

Pair 'stabbed by attacker in black'

A witness told the BBC he saw a man and woman being stabbed on Ilkeston Road at around 4am.

He said he heard "awful, blood-curdling screams" and there was a "black guy dressed all in black with a hood and rucksack grappling with some people".

He said the woman was shouting for help.

"I saw him stab the lad first and then the woman. It was repeated stabbing - four or five times. The lad collapsed in the middle of the road," the witness said.

"The girl stumbled towards a house and didn't move. The next minute she had disappeared down the side of a house, and that's where they found her.

"I'd say it all happened within five or six minutes. The attacker then just walked off up Ilkeston Road towards town, as calm as anything."

The man called police, who arrived in about five minutes, before paramedics tried to revive the pair for 40 minutes.

'I saw two people on the floor'

Another witness, who gave her name as Frances, told Sky News she heard a sudden bang and screaming as a white van drove into people in the city centre.

She said she "crossed over the road at Theatre Royal and got around 10 feet down the road when all of a sudden you heard a bang - which sounded like a vehicle hitting a bollard".

"I turned around and then saw the two people on the floor, on the road," she added.

"Someone was screaming, I think a gentleman ran over to help as well.

"Then it just went from there, the police were there straight away, then the ambulance arrived and they got the two people in the ambulance and got them sent off to whichever hospital."