Three people including a suspected gunman have been shot dead near a swimming pool.
The horror unfolded near Castle Swimming Pool in Spalding, on Tuesday, Lincolnshire Police said. No shots have been fired by officers.
Eyewitnesses reported hearing "dozens" of police cars and an air ambulance heading to the scene.
One woman, who did not wish to be named, said: "We heard all the police cars earlier this morning - they were absolutely everywhere, tearing around.
"We didn't hear any shots, nothing at all, only the dozens, literally dozens, of police cars. It must have been about half past nine or quarter to 10 when it started and there was car after car."
Another local, who asked not to be named, said an air ambulance was still outside the swimming pool more than an hour after the incident.
A force spokesman said: "We can confirm that there has been a firearms incident on Pinchbeck Road in Spalding, in the vicinity of the Castle Swimming Pool, in which three people have been fatally wounded, including the suspected offender.
"There is an ongoing police investigation and at this stage we are not looking for anyone else in connection with the incident. There is no indication that this is a terrorist-related incident and no shots have been fired by police.
"We would urge members of the public to stay away from the area at the present time."