A mass shooting has occurred at a Sikh temple in Oak Creek, Wisconsin. So far, at least four people have been reported shot, including the president of the temple.

There is a possible hostage situation involving children. A SWAT team entered the building before noon, but the Milwaukee County Medical Examiner's Office has not yet been called.

There may be as many as 20 to 30 victims inside.

Reports from inside indicate that there are anywhere from one to four gunmen. One has been described by a witness as "a white male, bald, with a heavy build. He was wearing a sleeveless T-shirt, according to Oak Creek Patch. He was last seen with two handguns."

This story is developing.

UPDATE:
 The Milwaukee Wisconsin-Journal Sentinel says that they have begun removing the injured from the temple's prayer room.

According to witness Ven Boba Ri, one of the temple's committee members, the shooter shot a priest outside the temple, then went inside and continued shooting. The president of the temple, Satwant Kaleka, was shot and taken to a hospital.

Ri told the paper, "It's pretty much a hate crime. It's not an insider."

UPDATE #2:
 Greenfield police chief Brad Wentlandt says the gunman has been "put down" after shooting an officer.

An officer arrived and engaged a suspect. That officer was shot multiple times. He is expected to survive. The officer exchanged fire with the shooter. That shooter was put down.

Police believe the situation is contained, but they are looking into the possibility of multiple gunmen.

UPDATE #3:
 CNN spoke to Carolyn Bellin, a spokesperson for Milwaukee's Froedtert Hospital, who said three men were brought in, all of them in critical condition. Early reports suggested that between eight and twenty people had been wounded.

UPDATE #4:
 CNN now says that six people were killed in addition to the gunman.

[Image via AP/Jeffrey Phelps]