British police in the city of Plymouth, southwest England, confirmed that “a number of deaths” were caused in a “serious accident with firearms”.
The accident occurred in Kiam district at around 18:10 GMT on Thursday.
Police said: “A number of dead people fell at the scene, and many other victims are receiving treatment.”
Johnny Mercer, Member of Parliament for Plymouth Moor View, described the incident in a tweet as “unrelated to terrorism”, saying the suspect was not a fugitive.
Police described the incident as serious, but said they believed it had now been contained.
Police urged citizens not to share photos of the accident site on social media or anywhere else.
Home Secretary Priti Patel tweeted her condolences.
She said: “The Plymouth incident is shocking, and I express my condolences to those affected.”
“I spoke to the chief of police and gave my full support,” she added.
“I urge everyone to remain calm, follow the advice of the police and allow our emergency services to continue their duties,” she said.
An eyewitness named Sharon, who lives not far from the scene of the accident and did not wish to give her full name, said what happened was “horrific and very sad”.
“First, we heard screaming, followed by gunshots, three or maybe four at first,” she said.
“This was when the shooter kicked in the door of a house and started shooting indiscriminately… He fled the house shooting as he ran, and proceeded to shoot a few people in the park away from the road,” she said.