Detectives have identified a man suspected of opening fire at a family planning centre in the US city of Colorado Springs, killing three people including a police officer.

Robert L Dear, 57, also allegedly injured nine people during the shoot-out at the Planned Parenthood clinic.

The stand-off began shortly before midday local time on Friday and ended six hours later when Dear gave himself up.

Officer Garrett Swasey and two unnamed civilians were killed during the shooting.

The 44-year-old was from the University of Colorado, about 10 minutes away from the clinic, and had responded to a call to help city officers.

The nine survivors are said to be in a good condition. None of the victims were patients or members of staff at the clinic.

Colorado Springs police spokeswoman Catherine Buckley said Dear had taken bags into the building, which was being searched amid fears they contained explosives.

She said he was armed with a "long weapon" with a shoulder stock such as a rifle, and some witnesses reported hearing automatic fire.

Many people were evacuated from the building, but others were unable to get out.

Joan Motolinia said his sister, Jennifer, called him while hiding behind a table in the clinic and that he could hear gunfire in the background.

"She was telling me to take care of her babies because she could get killed," he said of the mother of three.

Image: David Zalubowski / AP/Press Association Images

Quan Hoang, the owner of a nearby nail salon, told CNN that when he first heard shots fired he thought a local bank was being robbed.

"We see cops, SWAT, the bomb squad, a whole bunch of people just trying to take cover around the Planned Parenthood area," he said in a telephone interview.

"An officer came back in and said, 'Is everyone safe?' We asked him questions and he said they've barricaded him inside the Planned Parenthood and he was shooting out from the windows."

Planned Parenthood said it did not know if it was the target of the attack.

However, Vicki Cowart, president of its Colorado branch, 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 operates hundreds of clinics nationwide providing services such as contraception, abortions and STD testing.

The non-profit organisation - which was rocked by claims it sells aborted foetal tissue for profit earlier this year - has been repeatedly targeted by pro-life activists.