A heavy emergency services presence has been deployed in Plymouth amid a “serious firearms incident” resulting in a “number of fatalities”, Devon and Cornwall Police said.
Johnny Mercer, MP for Plymouth, Moor View, has called for calm from local residents.
He said a “serious and tragic” incident in Plymouth thought to involve several victims is “not terror related”.
Emergency services are at the scene in Keyham, where there have been unconfirmed reports of gunshots and of a number of fatalities.
Luke Pollard, MP for Plymouth Sutton and Devonport said he was awaiting confirmation of the number of victims, saying the situation looked like “a very grim day for our city and our community”.
Mr Mercer tweeted: “The incident is not terror related, and neither is the suspect on the run in Plymouth.
“Remain calm. It is for the Police to confirm further details. Do not repost chatter or gossip; work with them. We have the best cops in the land.”
In an earlier tweet, Mr Mercer said he was “aware of a serious and tragic incident unfolding in Plymouth.”
He added: “Please obey all instructions from the police and do not post rumour or speculation on social media.”
Devon and Cornwall Police said in a statement: “Police were called to a serious firearms incident in Biddick Drive, in the Keyham area of Plymouth at around 6.10pm today [Thursday 12 August].
“Officers and ambulance staff attended. There have been a number of fatalities at the scene and several other casualties are receiving treatment.
“A critical incident has been declared. The area has been cordoned off and police believe the situation is contained.
“Road closures are in place so please avoid the area.
“We are appealing to the public not to speculate or share pictures of the scene on social media or anywhere else.”
Priti Patel issues statement
Home Secretary Priti Patel tweeted: “The incident in Plymouth is shocking and my thoughts are with those affected.
“I have spoken to the Chief Constable and offered my full support. I urge everyone to remain calm, follow police advice and allow our emergency services to get on with their jobs.”