Washington: A gunman killed six people and left three others critically wounded in an attack on worshippers at a Sikh gurudwara (temple) in a Wisconsin suburb Sunday before being shot by a police officer.

The officer, who was sent to the temple in the Milwaukee suburb of Oak Creek, Wisconsin, after a 911 call about 10.25 a.m., was wounded but "returned fire, and that shooter was put down", Bradley Wentlandt, the police chief in nearby Greenfield, told reporters.

Investigators, who picked through the building afterward, found four bodies inside the temple and two other victims outside, plus the gunman, Wentlandt was quoted as saying by CNN.

Though early reports had suggested there may have been more than one attacker, he said officers had not identified any other gunmen.

The wounded officer, a 20-year veteran, was in surgery Sunday afternoon after being shot multiple times, but was expected to survive, Wentlandt said.

Carolyn Bellin, a spokeswoman for Milwaukee's Froedtert Hospital, said one of three men brought there from the incident was in surgery early Sunday morning, while another was in the surgical intensive care unit.

The third was being evaluated in the emergency room. All three were in critical condition.

"I just want to say this temple was built a number of years ago and there have never been any problems with this temple," Oak Creek Alderman Dan Jakubczyk said. "They've been a plus to this city and to my district."

As reports of the firing came in, the Indian Embassy got in touch with the National Security Council in Washington and deputed an official to visit the site to ascertain the situation on-the-spot.

The Embassy is seized of the situation and has been in touch with the NSC, it said in a statement. "Our Consulate General in Chicago too has been in close touch with the local authorities to monitor the situation."

Members of the police SWAT team have begun removing the injured from the temple's prayer room, the Milwaukee Journal-Sentinel reported.

Among those shot was Satwant Kaleka, president of the temple, Wentlandt told the Journal-Sentinel.