No motive is yet known for Wisconsin shooting, but members of Oak Creek Gurudwara have complained of past harassment

The shooting at a Sikh temple in Wisconsin will place new focus on a religion that is the fifth largest religion in the world with 27 million adherents, but it is one of the smallest faiths practiced in the US.

There are an estimated 250,000 Sikhs in the US, fewer than in the UK, which has about a fifth of the US's population.

About 3,000 Sikh families live in southeastern Wisconsin, according to local reports. Local Sikhs had met in a rented space on the south side of Milwaukee until 2007 when the Oak Creek Gurudwara, as Sikh temples are known, was built. The 17,500 square-foot Gurudwara has parking for a hundred cars.

Sikhism was founded in South Asia more than 500 years ago. Observant Sikhs do not cut their hair, and male followers often cover their heads with turbans and refrain from shaving their beards.

Members of the Sikh community in the US were physically attacked after the 9/11 terrorist attacks by racists who were also attacking America's Arab and Muslim communities. Witnesses to the shooting on Sunday have expressed fears that once again their community may have been targeted as part of a hate crime.

One of the temple's committee members, Ven Boba Ri, told Milwaukee's Journal Sentinel that people inside the temple had described the gunman as a white male in his 30s.

"We have no idea," he said of the motive. "It's pretty much a hate crime. It's not an insider."

Ri said the man walked up to a priest who was standing outside and shot him. Then he went inside and started shooting.

"It's sad, I don't know how to describe it," said Ri. "Sikhism is such a peaceful religion. We have suffered for generations, in India and even here."

"We're all the same," temple member Jaswinder Schandock told the Journal. "Everybody has the same blood."

State representative Josh Zepnick and district attorney John Chisholm visited the Oak Creek Temple last year after calls from local Sikhs whose businesses had been targeted by robbers and vandals. Zepnick said: "It's unacceptable that they, or any law-abiding business owner, be the target of what appears to be an escalating pattern against certain businesses and segments of the population."

As witnesses to the Oak Creek attack worried that there may have been a racial motive to the attack, the New York police department said Sunday that it was stepping up protection of Sikh community.

The Joint Terrorism Task Force, a collection of federal, state and local law enforcement, was called in to Oak Creek on Sunday. While the task force's main job is combating terrorism it also responds to mass shootings and it is not yet clear how this tragedy will eventually be categorized.