"The area has been cordoned off and police believe the situation is contained."
Several of the shooter's relatives along with unconnected members of the public are believed to be among the victims, reported the Mail.
Dozens of locals have reported a "shooting" online, with footage circulating online appearing to show a bloodied victim on the ground surrounded by armed police.
In one video posted to social media an armed officer can be heard telling members of the public to "walk away" from the scene.
Police dogs are also on scene searching the area within the cordon
'A grim day'
Home Secretary Priti Patel said: "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."
Local MPs have described the situation s "very serious", adding that it is a "grim day" for their community.
Luke Pollard MP said: "There looks to be a very serious situation happening in Keyham. Please can everyone stay safe, stay indoors and follow police advice.
"Awaiting confirmation of number of victims but this looks like a very grim day for our city and our community.
"Please can I ask that you think of the families and our community and not share any images or videos of any of the victims."
Really worrying news coming out of Keyham in #plymouth. Please can everyone stay safe, stay indoors and follow police advice.
South Western Ambulance spokesman said: "We were called at 6.12pm to an ongoing incident in Plymouth.
"We responded to the incident with a significant number of resources, including Hazardous Area Response Teams, multiple ambulances, air ambulances, multiple doctors and senior paramedics."
Devon and Cornwall Police has been contacted for more information.