OAK CREEK: A gunman opened fire at a Sikh temple in the northern United States on Sunday, triggering a shootout which left him and at least six others dead, local police said.

“An officer arrived on the scene, engaged the shooter and was shot multiple times,” Greenfield police Chief Brad Wentlandt told reporters in Oak Creek, outside Milwaukee, Wisconsin.

“That shooter was put down.”

”At this time, we have not identified any additional gunmen,” he added, contradicting reports of multiple shooters but stressing the situation was “extremely fluid” and that officers were still securing the scene.

Four people were killed inside the temple and three others outside. Wentlandt had said earlier that a suspect had been “put down” outside the temple after shooting a police officer. He said the officer was being treated at a local hospital and was expected to survive.

Three adult men in critical condition were being treated at Froedtert Hospital, a spokeswoman told AFP.

“We've heard the scene is still unfolding, so we're prepared for more”victims, the hospital's chief medical officer Lee Biblo told CNN.

Police tactical units were on the scene, along with officers from multiple law enforcement agencies, including the Federal Bureau of Investigation.

The president of the temple, Satwant Kaleka, was shot and was taken to a hospital, according to The Milwaukee Journal Sentinel. It said there were believed to be as many as 20 to 30 victims.

The newspaper said that at one point the head priest of the temple, which had a congregation of between 350 and 400 people when it was formally established in 1999, was locked inside a restroom with a cell phone.

Witness Suni Singh said up to four gunmen may be hiding inside the temple since the shooting took place around 10:30 am (1530 GMT).

“My friend called and said 'I heard the shot, and two people falling down in the parking lot.' He saw the shooter reloading the gun again,” Singh told Newsradio 620 WTMJ.

About 50 people were at another temple in nearby Brookfield for a morning service and many went outside after learning of the shooting in Oak Creek, The Milwaukee Journal Sentinel said.

Temple committee member Ven Boba Ri said that based on communication with people inside the temple, the shooter was a white male aged in his 30s.

“We have no idea” what the motive could be, he told the newspaper. “It's pretty much a hate crime. It's not an insider.”According to religious tradition, Sikh Indians wear turbans to cover their uncut hair and sport long beards.

In the United States they have often been mistaken for Muslims and have been targeted by anti-Islam activists, particularly after the September 11, 2001 attacks on the United States.

Sunday's shooting also bore some similarities to a March 2005 incident in Brookfield that saw a gunman kill seven worshippers and himself during a church service at a hotel.