A major incident is currently unfolding in Plymouth with the Hazardous Area Response Unit (HART), police and air ambulances attending.
Eyewitnesses have claimed that they heard "loud bangs" and gun shots".
According to recent reports, the three ambulances, not four as originally thought, have landed in North Prospect area of Plymouth this evening.
An eyewitness said: "Looks to be some sort of serious incident north of St Levan’s Road.
"Both Devon and Cornwall Air Ambulances have landed and a lot of police/emergency unmarked heading that way.
"Three air ambulances and NPAS now."
Another added: "Have 2 medical helicopters and police helicopter flying around north prospect area."
South Western Ambulance Service wrote on Twitter: "We were called at 18:12 to an ongoing incident in Plymouth. We responded to the incident with a significant number of resources, including Hazardous Area Response Teams (HART), multiple ambulances, air ambulances, multiple doctors and senior paramedics."
Luke Pollard, MP for Plymouth, said: "Really worrying news coming out of Keyham in Plymouth.
"Please can everyone stay safe, stay indoors and follow police advice."
According to reports air ambulances from across the country, including Southampton and Dorset, are at the scene.
A nearby school sports centre has been told close down with people indoors being ordered to leave.
Cordons, which are constantly expanding, have been put in place around a block of flats to prevent pedestrians from walking along.
The road on which the incident took place has now completely closed.
Johnny Mercer, MP for Plymouth Moor View, said: "I'm aware of a serious and tragic incident unfolding in Plymouth.
"Please obey all instructions from the Police and do not post rumours or speculation on social media."