LONDON, United Kingdom -- Six people, including the suspected gunman, died Thursday during or shortly after a ''serious firearms incident'' in the southwestern English city of Plymouth, police said.

Devon and Cornwall Police declared a ''critical incident'' in the Keyham area of Plymouth early Thursday evening following the shooting, but later said it was not being considered terrorism related.

Officers had responded alongside other emergency services, including air ambulance staff, to reports of gunshots in the residential neighborhood near some of the city's docks.

''Two females and two males were deceased at the scene,'' the force said in an update early Friday after hours of uncertainty around the incident.

''A further male, believed to be the offender, was also deceased at the scene.''

Police added another female treated at the scene died a short time later in hospital.

''All are believed to have died from gunshot wounds,'' the force said.

It was unclear how the victims and suspected perpetrator were connected, with many details of what unfolded in the city of around 262,000 residents in the sleepy southwest English county Devon remaining unclear.

''Police would stress this is not a terrorism related incident,'' the force added, noting officers were not looking for anyone else in connection with it.

''Investigations are continuing,'' Devon and Cornwall Police said.

Interior Minister Priti Patel called the incident ''shocking'' and said her thoughts were ''with those affected'' but did not reveal further details of what occurred.

''I have spoken to the Chief Constable and offered my full support,'' she tweeted.

''I urge everyone to remain calm, follow police advice and allow our emergency services to get on with their jobs.''

'Randomly started shooting'

British media said local residents had reported hearing loud bangs and gunshots before police swarmed the area.

Witness Sharron, who did not want to give her full name, told the BBC she had heard shouting followed by several gunshots.

''This was when the shooter kicked in the door of a house and randomly started shooting,'' she said.

''He ran from the house shooting as he ran and proceeded to shoot at a few people''.

Robert Pinkerton, a second witness, told the British broadcaster he ''walked around the corner'' and ''bumped into a bloke with a shotgun'' dressed all in black.

South Western Ambulance Service said it had responded to the incident with a significant number of resources, including Hazardous Area Response Teams, air and ground ambulances, multiple doctors and senior paramedics.

Luke Pollard, a local MP, said the situation looked like ''a very grim day for our city and our community''.

''Please can everyone stay safe, stay indoors and follow police advice,'' he added.

Keir Starmer, leader of the main opposition Labour Party, said ''tragedy has hit Keyham''.

''I pay tribute to our emergency services who ran towards events we'd all run from,'' he added.

Mass casualty shootings are rare in Britain, where most police officers are unarmed, while southwest England -- a popular domestic holiday destination -- is typically known as a tranquil part of the country.

Plymouth is home to the biggest naval base in western Europe, including nuclear submarines and large warships.