Police have been searching for a gunman who opened fire near a Planned Parenthood clinic in the US state of Colorado.

At least three officers were injured but it was not known if anyone else was wounded in the attack in Colorado Springs, authorities said.

Police Lieutenant Catherine Buckley said authorities also did not know where the gunman was located or whether the shooter had taken any hostages.

"We can't confirm where the shooter is at this point," she said.

Asked if the gunman had taken hostages, Lt Buckley told reporters: "There is that possibility. There are a lot of possibilities with this scenario."

Authorities received a call of shots being fired at the Planned Parenthood clinic before noon local time. Planned Parenthood is a US women's health care provider that offers abortions at some clinics.

Responding officers exchanged gunfire with the shooter, Lt Buckley said, adding that it was not known if the shooting had any connection to Planned Parenthood.

Ambulances and police vehicles were lined up at the nearby intersection and police told people to stay away from the shooting scene because it was not secure.

Mike Pelosi, who works at a deli at a nearby King Sooper grocery store, said he heard over the store's loudspeaker just before noon that nobody could leave the store.

Mr Pelosi said customers and store employees were confused about what was going on but not panicked.

He said a couple dozen customers were standing near the store entrance waiting for instructions.

The Planned Parenthood clinic is located next to a medical office building and near a shopping complex.