Police are responding to reports of a "serious incident" in Woolwich, south London.
Initial reports suggest a man has been attacked, and pictures posted on Twitter appear to show three people lying on the ground.
Scotland Yard said the incident took place in John Wilson Street, at 14:20 BST.
Police said they were called to reports of an "assault".
London Ambulance Service said an air ambulance and four crews were at the scene.
Police say the area around John Wilson Street has been shut down.
Posts on Twitter claim one man was attacked with a machete, but police have not confirmed this.
Firearms officers are at the scene and a cordon has now been established.
Local primary school head teacher David Dixon tells the BBC News Channel he saw a body in the road and "there were gun shots after that".
He instructed staff to lock all the gates of his school and an air ambulance landed in the playground.
Most of the children have now gone home. Mr Dixon said everything inside the school was "calm and orderly".
Eyewitnesses say two men attacked another man with a "machete-style knife".
Reports also suggests shots were fired, although details are not yet clear.
A witness claims two men in a car ran over another man, then got out of the car and attacked him, the BBC's Matt Prodger reports.
It is claimed the victim was wearing a Help for Heroes charity T-shirt, but this has not been confirmed.
Local MP Nick Raynsford says one person has been killed in the incident and two others have been seriously injured.
Local MP Mr Raynsford says a soldier serving at a nearby Army barracks has died in the incident.
Mr Raynsford tells BBC Radio 5 Live: "What I have heard from both the borough commander and the station commander of the barracks indicate this was a serious incident involving a number of weapons including firearms.
"I am told that one of the individuals involved in the incident... is a soldier serving in the Army in the barracks."