OAK CREEK, Wis. — Members of the Sikh Temple of Wisconsin had just started to gather for services Sunday morning when their peaceful world was shattered.

As worshippers gathered to eat, sing and pray, a man entered the temple in a suburb just south of Milwaukee along Lake Michigan and started firing, police said.

The surprising cracks of gunfire sent many inside scurrying for a hiding place, including a group of women who sought refuge in a pantry while they telephoned relatives and instructed them in whispers not to come to the temple.

The gunman shot and killed six people and injured three more, including a police officer, police said.

A 20-year veteran of the Oak Creek Police Department responded to a 911 call around 10:25 a.m. and was tending to a victim outside the temple when the gunman ambushed him, Police Chief John Edwards said. Another officer shot and killed the gunman, he said.

Police refused to speculate on the gunman's motive, but Edwards called it an act of "domestic terrorism."

Late Sunday, the investigation appeared to move beyond the temple as police, federal agents and the county sheriff's bomb squad swarmed a neighborhood in nearby Cudahy and evacuated several homes. Police roped off four blocks around a duplex, but the building's owner, Kurt Weins, said authorities would not say why they were there or if it was related to the shooting.

Tattoos on the body of the slain gunman and certain biographical details have led the FBI to classify the incident as "domestic terrorism," according to a White House official, the Chicago Tribune reported. He would not say if the gunman is believed to belong to a hate group or some other violent group, as the investigation, which was handed to the FBI on Sunday afternoon, is still unfolding.

"We don't know much about the motive at this point," said a federal law-enforcement official who had been briefed on the early planning for the case.

Tom Ahern, a spokesman for the ATF, told reporters the suspect was a 40-year-old white man. He did not provide additional details and would not confirm reports the suspect had a tattoo.

For hours after the incident there was a chaotic scene outside the temple as family, friends and congregants gathered to wait for details, which came slowly. After the shooting, platoons of police and FBI agents interviewed witnesses in the basement of the bowling alley across the street but prohibited them from initially contacting their family or friends.

Edwards said he did not have details on the total number of people inside the temple at the time of the attack. He confirmed that authorities found weapons on the scene but declined to say how many or what kind.

One shooting victim was Satwant Singh Kaleka, the president of the temple, said his son, Amardeep Kaleka. He was told his father walked through the building to confront the shooter in the lobby or near the office, tried to tackle him and was shot, Kaleka said.

He said he was also told that a priest near his father during the incident was shot in the hip or leg and was "bleeding profusely."

The gunman opened fire about an hour before an 11:30 a.m. service, which temple member Harvinder Ahuja estimates about 350 people attend each Sunday.

When asked why police took some time to get inside the building, Edwards said officers had to act cautiously, with the expectation that there might have been more than one shooter.

After the shooting began, frantic posts on Twitter asked people not to call loved ones trapped inside on their cellphones.

The public scenes of carnage came as the nation is still reeling from a mass shooting two weeks ago in which a gunman killed 12 people and injured 58 at a movie theater in Aurora, Colo. The pain was especially felt among the nation's more than 500,000 adherents of the Sikh faith, most of whom are first- or second-generation immigrants from India, where Sikhism was founded several centuries ago as an offshoot of Hinduism.

Sikh men tend to stand out because of their beards and colorful turbans, which are ritually wrapped around uncut hair, and leaders in the community say they are sometimes confused with Muslims and viewed with suspicion. After the attacks of Sept. 11, 2001, there were scattered reports nationwide of harassment or attacks on Indian Sikhs, including the killing of an unarmed man in Phoenix.

This year marks the 100th anniversary of the first Sikh temple in the United States. The Sikh Temple of Wisconsin was established in 1997 with 20 to 25 families. There are now 350 to 400 people in the congregation, according to the temple's website.

Police in New York and Chicago issued statements saying they were giving Sikh temples in those cities additional attention as a precaution after the shooting.

Valarie Kaur, who chronicled violence against Sikh Americans in the 2006 documentary "Divided We Fall," was returning to her home in New Haven, Conn., after speaking at a White House conference Friday when she heard about the shootings.

Even though the gunman's motives were a mystery Sunday, Kaur said the shootings reopened wounds in a community whose members have found themselves frequent targets of hate-based attacks since Sept. 11.

"We are experiencing it as a hate crime," she said. "Every Sikh American today is hurting, grieving and afraid."

Jaswinder Singh, president of the Bothell-based Gurudwara Sikh Centre of Seattle, said Sunday's shooting in Wisconsin was a "tragic event" that could've happened anywhere, targeting members of any faith.

"We are saddened and hurt by this tragic event. It's just one of those isolated things. We feel for the victims and their families," Singh said Sunday. "We are grateful for the police officer who put himself in harm's way" and the officer "who took care of the shooter."

Congregants briefly met to discuss the shooting on Sunday and plan to contact police to see if any security precautions are warranted, he said.

"For me, it's like just another crazy man," Singh said, referencing the fatal shootings in Colorado. "But I imagine others in the congregation are a bit worried."

Sikhs are "a peace-loving people," he said. "There may be some bias based on appearance, but I still say this is one of the greatest nations on Earth. There's definitely more love than hate."

Compiled from Chicago Tribune, The Washington Post, The Associated Press and The New York Times reports and material from Seattle Times staff reporter Sara Jean Green.