British police said a man had been arrested on suspicion of murder after three people were found dead on the street in the city of Nottingham and three were in hospital after an attempt to run them over with a van.
Police said two people had been found dead on one road in the centre of the city just after 4:00 am (0300 GMT) before officers were alerted to another incident not far away where someone driving a van had tried to run over three people.
They are being treated in hospital.
Another man was also found dead on a road just outside the city centre.
"This is a horrific and tragic incident which has claimed the lives of three people," Chief Constable Kate Meynell said.
"We believe these three incidents are all linked and we have a man in custody. This investigation is at its early stages and a team of detectives is working to establish exactly what has happened."
A 31-year-old was arrested on suspicion of murder and was in police custody. No indication was given of motive, but the police statement made no mention of counter-terrorism officers being involved.
"It is too early to comment on casualties or the exact nature of the incident," the East Midlands Ambulance Service said.
Inside one of the police cordons, officers guarded a white van that had its passenger door wide open with a rucksack lying on the ground beside it, and damage to its bonnet and windscreen.
At Ilkeston Road, where the two people were found dead, medical equipment was strewn across the street.
"I am being kept updated on developments. The police must be given the time to undertake their work," Prime Minister Rishi Sunak wrote on Twitter, calling the incident "shocking".
Several major roads were closed and the Nottingham tram network was suspended. Members of the emergency services were visible across the city.
Meynell said much of the city would remain sealed off while the investigation continued.