COLORADO SPRINGS, COLORADO: Police arrested a gunman who stormed a Planned Parenthood abortion clinic in Colorado Springs on Friday and opened fire with a rifle in a burst of violence that left at least 11 people injured, including five officers, authorities said.

The suspect, who engaged in a protracted gun battle with police, surrendered to officers inside the building about five hours after the clinic siege began.

Authorities did not report any fatalities, but a police spokeswoman, Lieutenant Catherine Buckley, said police were still searching for possible victims who might have been left behind in the clinic as the building was evacuated.

"I do not have any confirmation of fatalities at this point," Buckley said.

A Reuters photographer at the scene saw a man in a white T-shirt, with his hands cuffed behind his back, being taken out of an armoured police vehicle and placed in an unmarked squad car. Authorities said they did not know the suspect's identity but believed he acted alone.

His capture was first confirmed by the city in a message posted to its Twitter account. Police elaborated on the circumstances in a news conference moments later.

"We did get officers inside the building. They were able to shout to the suspect and make communication with him and at that point they were able to get him to surrender and he was taken into custody,” Buckley said.

An hour earlier, police said progress in securing the building was slowed by the fact that the gunman brought "some bags" with him into the clinic and left several items outside, all of which needed to be checked for possible boobytraps or explosives.

After the arrest, Buckley said it would take hours more, and perhaps days, for investigators to fully process the crime scene.

Police swarmed the area around the building after an emergency call reporting shots fired at about 11:30 a.m. Mountain Time (1830 GMT), and officers ultimately confronted the suspect inside the building, Buckley said.

Television footage aired by CNN showed a number of clinic staff and patients being escorted safely into police vehicles from the building, which lies on the northwest side of Colorado Springs, about 70 miles (112 km) south of Denver.

The FBI and agents from the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives were assisting local law enforcement investigators.

President Barack Obama was notified of the shooting by his Homeland Security adviser, Lisa Monaco, and "will be updated on the situation as necessary, a White House official said.

The Planned Parenthood centre provides abortions, screening for sexually transmitted diseases, pregnancy testing and other services, according to its website.

"We don't yet know the full circumstances and motives behind this criminal action," Vicki Cowart, president and CEO of Planned Parenthood Rocky Mountains, said in a statement.