A man was shot and killed by police on Tuesday night after stabbing four people, two of whom later died, in twin attacks at a house and shopping mall in the US state of Massachusetts, state police said.

Two people were stabbed at a mall outside Boston by an assailant who crashed a car into the front of a store after two other people were stabbed at a nearby residence, police said.

The suspect died after being shot by an off-duty law enforcement officer at the Silver City Galleria, Massachusetts State Police said in a statement.

State police said in a Tweet later on Tuesday evening that the suspect and two of his victims had died, and that more information would be released by a county prosecutor.

Taunton Fire Department dispatcher Mike Marshall said reports started coming in around 6:37 p.m and that the department sent out "a lot" of ambulances.

Witnesses told local television station WHDH-TV that they saw people running out of the mall and heard gunfire. The station reported that people in the area, about 40 miles (64 km) south of Boston, saw police officers with guns drawn and that the mall had been evacuated and put on lockdown.

The motivation behind the attacks was unclear. A number of state and local police units were at the crime scenes, authorities said.

A representative of the mall, which has 125 stores, a 12-unit food court, restaurants and a cinema, could not immediately be reached. – Reuters