Lieutenant Catherine Buckley of the Colorado Springs Police Department confirm​ed two civilians and a University of Colorado campus police officer at Colorado Springs were among the dead.

The Colorado University's Colorado Springs (UCCS) campus chancellor Pam Shockley-Zalabak, confirmed the police officer killed was 44-year-old Garrett Swasey.

Local media outlets reported also reported that four civilians and five police officers were taken to hospital with gunshot wounds.​

12:54pm AEDT:  Two people have reportedly been killed in the shoot-out siege at the Colorado Springs abortion clinic, according to local media.

Local television station KKTV reported that a university campus police officer had attended to support the Colorado Springs Police, but was killed. Television station 9News in Denver reported that one officer and one civilian were dead.​

Colorado University's Colorado Springs (UCCS) Chancellor Pam Shockley-Zalabak said in a statement: "We at UCCS are saddened by the tragic events today at the offices of Planned Parenthood in Colorado Springs, about 10 minutes southwest of campus."

She said the officer had been on duty at the time at the university campus and responded in support of Colorado Springs Police Department when he came under fire.

11:36am AEDT: Police have taken a person into custody after a five-hour gun siege at an abortion clinic in Colorado Springs.

Five police were injured in the shoot-out and 11 people were taken to hospital.

Police are now combing through the Planned Parenting clinic and explosives experts are needed to assess bags brought into the building by the gunman.

The Mayor of Colorado Springs, John Suthers confirmed police had taken the person into custody at about 4.50pm local time. 

Local reports suggests more than 115 officers are at the abortion clinic.

11:10am AEDT: There are unconfirmed reports a gunman who went on a shooting rampage at a Colorado Springs abortion clinic is in custody.

There were fears the gunman, who shot at least four police officers and injured five civilians, had taken items into the clinic to create an explosion.

10.48am AEDT: There are fears a gunman, who has shot at least four police officers and injured five civilians, brought items into a Colorado Springs abortion clinic to create an explosion, according to reports.

Police spokeswoman Lieutenant Catherine Buckley said there were reports of propane gas cylinders outside the building but it is unclear whether the gunman brought them in. She said the gunman had taken bags into the Planned Parenthood building in the state of Denver in the United States.

The shooter has been engaged in a gun battle with police and remains barricaded in the clinic.

Police have used an armoured vehicle to evacuate people, while others were able to escape out windows and side doors.

However, Lieutenant Buckley told a media conference that some patients, staff and police remained inside.

The situation is now contained to the building, but police are yet to speak to the gunman.

9.44am AEDT: A shooter is engaged in a gun battle with police near an abortion clinic in Colorado Springs in the United States, according to reports.

The gunman is barricaded inside the building and firing at police after injuring at least four police officers.

The New York Times reports that he is exchanging gunfire with police with the confrontation heard on police scanners.

"We're exchanging gunfire," one officer was reported to have said, "We are trying to keep him pinned down."

"Put gunfire through the walls," came a reply. "Whatever, we got to stop this guy."

Police spokeswoman Lieutenant Catherine Buckley told reporters the shooter was a white man dressed in a trench coat and armed with an assault rifle.

The Denver Post reports that local man Joan Motolinia said his sister Jennifer, who had an appointment at the clinic, was hiding under a table when he last spoke to her on the phone. He heard gunshots before she hung up. He had not heard from her since.

The gunman went inside the Planned Parenthood clinic in Colorado Springs on Friday, and opened fire repeatedly on police officers through windows, USA Today reports.

Police and media reports say several people had been hit.

Media outlets have reported that four police officers have been injured and that civilians have also been taken to hospital.

"Rounds are coming through the window," one police officer told the dispatcher on the police scanner.

Mike Violette, executive director of the Colorado Fraternal Order of Police, said on Twitter: "Shooter barricaded in planned parenthood & multiple victims."

One police officer was shot in the hand, and another was also wounded, law enforcement authorities told local station KKTV.

The gunman was described as wearing a long coat with a hunting-type hat.

The wounded are not confined to the abortion clinic, ambulance authorities say one person was wounded at a local eye clinic nearby, The Gazette, a Colorado newspaper, reports. The newspaper said one victim was taken by stretcher to an ambulance.

The Gazette also reports that a police car rear window was shot out after an officer tried to drive by to get a look at the gunman.

Ten ambulances are lined up along the street waiting for the injured.

An injured police officer was taken on a stretcher from an armoured police car to a waiting ambulance.

A police intelligence officer at the scene, Lietenant Catherine Buckley has told a local reporter that anyone in the vicinity of the shooter should "shelter in place".

She did not rule out the possibility of hostages or that there could be more than one gunman.