British police announced the arrest of three men after a car exploded in front of Liverpool Women's Hospital, in the city centre, killing one man and injuring another Sunday morning.

Officers arrested the three men, aged 29, 26 and 21, in Liverpool's Kensington district under the anti-terrorism laws, Greater Manchester Police said in a tweet.

The man killed in the blast has not yet been identified, the statement said. The injured man, who was driving, was in a stable condition in hospital.

Counter-terrorism police in the region were working closely with the Liverpool force, the statement added.

Merseyside police, who cover Liverpool, said in a separate statement that while anti-terrorism police were leading the investigation, the blast has not yet been declared a terrorist incident.

They were keeping an open mind as to the cause of the blast, the force added.

"So far we understand that the car involved was a taxi which pulled up at the hospital shortly before the explosion occurred," said Merseyside police.

'Calm, but vigilant' 

"We would urge the public to remain calm (but vigilant)," Merseyside Police added.

On Twitter, Prime Minister Boris Johnson praised the emergency services for their work on the incident so far.

Interior Minister Priti Patel tweeted earlier that police were keeping her up to date on developments.

"Our police and emergency services are working hard to establish what happened and it is right they are given the time and space to do so," she added.

The blast had happened just before 11:00 am (1100 GMT), said police.

Images posted on news and social media showed the cordoned-off blast site, and heavy grey smoke rising.

Phil Garrigan, the head of the Merseyside fire service, said that by the time their engines arrived at the scene, the fire was well under way.

One person had managed to get out of the vehicle before the fire took hold, but a second had died, he added.

A statement from Liverpool Women's Hospital said that, where possible, patients were being diverted elsewhere.