Police surrounded a district where a Boston marathon suspect was believed to be hiding after a burst of automatic gunfire, media reports said.
Police squads and armored personnel carriers raced to the district and police helicopters buzzed overhead after the gunfire.
The Boston Globe quoted a source as saying police had 19-year-old Dzhokhar Tsarnaev “pinned down.” CNN said police believed they had the suspect surrounded.
WCVB television said a body had been found on a boat in the district.
Gunfire erupted in the district only minutes after police told a press conference they believed that Tsarnaev had escaped a mass dragnet thrown over Watertown.
Chechen brothers Dzhokhar and Tamerlan Tsarnaev are the main suspects in the Boston marathon bombing on Monday in which three people were killed and about 180 injured.
Tamerlan, 26, was killed in a shootout with police in the early hours of Friday after an earlier gunbattle in which a police officer was shot dead.