Three people have been killed - and another three injured - in connected "horrific and tragic" attacks in Nottingham.
Two people, believed to have been stabbed, were found dead by police in Ilkeston Road just after 04:00 BST.
Officers were then called to Milton Street where a van had attempted to run over three people.
Police, who have arrested a man on suspicion of murder, later found a man dead in Magdala Road.
The 31-year-old arrested man is in custody and several police cordons are in place in the city centre.
Amed officers also raided a property in Ilkeston Road shortly before 13:00.
Nottinghamshire Police said the three people injured in the van attack in Milton Street were being treated in hospital.
Chief Constable Kate Meynell said the force believed all three incidents were linked.
"This is an horrific and tragic incident which has claimed the lives of three people," she said.
"This investigation is at its early stages and a team of detectives is working to establish exactly what has happened.
"We ask the public to be patient while inquiries continue."
An eyewitness told the BBC he witnessed a young man and young woman being stabbed in Ilkeston Road, close to the junction with Bright Street, at about 04:00.
The man, who asked to remain anonymous, said he heard "awful, blood-curdling screams" and saw a man dressed in black, with a hood and rucksack, "grappling with some people".
"It was a girl, and a man or boy she was with - they looked quite young," he said.
"She was screaming 'help!' I just wish I'd shouted something out of the window to unnerve the assailant.
"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 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."
Carl Cassidy said he witnessed two people get knocked over by a white van while dropping his wife off at work.
"We pulled up outside the Theatre Royal and as my wife opened the car door we heard an almighty bang," he said.
"A white van was heading for my car but it swerved and missed us by inches, mounting the pavement.
"I got out of the car and saw two people lying on the ground. The lady seemed OK, she was shaken but sitting up and OK. The man who was hit harder seemed a bit worse.
"He was on the other side of the road and people were helping to put him in the recovery position.
"Police were following the vehicle but stopped to tend to the injured.
"The van drove off and within seconds three more police cars arrived at the scene."
NicChuter lives in Mapperley Road, close to the junction of Woodborough Road, not far from where a man was found dead in Magdala Road.
The former emergency planner said he was greeted by armed police officers as he left the house.
He said: "[The] first thing we saw this morning when I took the children to nursery was someone calling me over with a very large gun saying 'hello, what are you up to?'
"We're not able to use the car as it's being counted as part of a crime scene, so everything within the cordon is staying put."
Prime Minister Rishi Sunak thanked the emergency services and said he was being updated on developments.
"My thoughts are with those injured, and the family and loved ones of those who have lost their lives," he said.
Home Secretary SuellaBraverman said she was "shocked and saddened" by the deaths, adding she had spoken to Nottinghamshire Police's chief constable and was "receiving regular updates".
Labour leader Sir Keir Starmer also sent his "thoughts to all those affected and to the emergency services who are responding".
Media caption,
Video shows police cars on Ilkeston Road at dawn
A damaged white Vauxhall Vivaro van and a cordon could be seen in Bentinck Road, Nottingham, which BBC Verify has confirmed is where an arrest took place.
It is not yet known if it is the same van that was involved in the incident.
A statement from the city's three Labour MPs - Lilian Greenwood, Nadia Whittome and Alex Norris - said: "Awful news for our city to wake up to today.
"Our community's thoughts and prayers are with all those affected.
"Our gratitude is with our blue light responders for their work today also."
Nottingham City Council leader David Mellen said: "Ours is an overwhelmingly peaceful and tolerant city where people get along with one another and it's incomprehensible that such dreadful violence has happened here.
"I'm grateful to the police for swiftly making an arrest and for all the emergency services responding to this tragic situation and keeping us safe."