Four police officers have been injured in an exchange of gunfire with a lone gunman, in or near a Planned Parenthood clinic in Colorado Springs. One police officer was shot in the hand, law enforcement told KKTV. Three of the injured officers have been moved to safety, while police are still trying to move the fourth out of harm's way. Colorado Springs police spokeswoman Catherine Buckley told reporters a fifth officer had also possibly been injured.

A police dispatch quoted by the Colorado Springs Gazette said there are also at least four civilian casualties in the attack by a lone gunman at the building in Centennial Blvd. It is not clear how serious their injuries are. It is feared some people in the clinic may have been taken hostage, but this is as yet unconfirmed.

The newspaper quoted police radio as saying a gunman in a long coat and wearing a "hunting-type" hat had begun shooting out the back window of his vehicle as an officer approached. "Rounds are coming through the window," one police officer reportedly told a dispatcher.

Colorado Springs police spokeswoman Catherine Buckley told reporters: "We do not have the shooter at this point. We do consider this still an active situation. There could be hostages and there could be an additional shooter at large," she said.

"There are a lot of possibilities with this scenario. As I said, it is very active and we are working our way through it."

She said the suspect had brought items with him to the building which authorities would need to establish were not explosive devices. "The officers inside the building have encountered the individual," she said. "They were exchanging gunfire."

It was not immediately clear whether Planned Parenthood was the target of the shooting. "We're not sure what the connection is to Planned Parenthood, but that was the original address we received for the call for service," Buckley said.

Police responded to a call from Planned Parenthood at 11.38am local time, Buckley said. The gunman, whose motives are unknown, was thought to be armed with a long gun. Ms Buckley added that they were trying to locate the suspect and could not confirm reports he was barricaded inside the clinic at Centennial Blvd.

The gunman has been described as a white male who is about 6 feet tall with a white beard.

Local TV station KKTV reported that nine people have been taken to two local hospitals, the city's Penrose hospital and Memorial hospital, also in Colorado Springs. At least eight ambulances are on standby at the scene.

Earlier, the US police department confirmed in a tweet that it was responding to a call about gunfire at the family planning clinic in Centennial Blvd. "The area is NOT secure," the tweet added warning locals to stay away from the area.

President Barack Obama has now been briefed about the unfolding active shooter situation in Colorado, the White House stated.

Planned Parenthood said it was monitoring Friday's situation, but did not know if it was the target of the attack. Vicki Cowart, president of Planned Parenthood Rocky Mountains, said in a statement: "We share the concerns of many Americans that extremists are creating a poisonous environment that feeds domestic terrorism in this country."

Planned Parenthood is a US family planning group with clinics nationwide providing services such as contraception, STD testing and abortions. The Colorado Springs branch has been the site of a number of recent protests.