Police said two people had been found dead on one road in the centre of the city just after 4 a.m. (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 in a road just outside the city centre.

"This is an 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 the motive for the incident, 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.

One woman identified as Lynn told BBC TV she had seen a van hit a man and a woman who were left lying in the street.

"He went straight into these two people. The woman went on the kerb, the man went up in the air. There was such a bang. I wish I never saw it. It's really shaken me up."

British Prime Minister Rishi Sunak thanked the police and emergency services for their response to the shocking incident in Nottingham and said police must be given the time to do their work.

"My thoughts are with those injured, and the family and loved ones of those who have lost their lives," he wrote on Twitter.

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.

"Awful news for our city to wake up to today," Alex Norris, a lawmaker for Nottingham, said on Twitter. "Our community’s thoughts and prayers are with all those affected."