Two hospitals are treating nine patients from the active shooting scene in Colorado Springs, NBC News reports.
The total number of civilian injuries is unclear.
A patient trapped inside the Planned Parenthood clinic as a gunman began shooting asked her brother to look after her babies in case she did not survive, local media have reported.
Joan Motolinia said that he got a short phone call from his sister Jennifer, aged 28, as she hid underneath a table after shooting started this morning.
"She was very afraid," he told the Denver Post newspaper. "She was telling me to take care of her babies.”
Mr Motolinia said he heard gunshots in the background during the short call. She hung up after around two minutes, and it is not known if she managed to escape the building.
The gunman is surrounded in the Colorado Springs abortion clinic, sources have told NBC News.
Police say the attacker is still shooting from inside the building, confirming that with at least four officers have been injured.
Earlier reports suggested at least three civilians were also being treated in local hospitals.
Police have said a fourth officer has been injured in a stand-off with a gunman at a Planned Parenthood clinic in Colorado Springs, according to reporters at the scene.
Officers had earlier confirmed at least six injuries, including three officers and three civilians.
Police in Colorado Springs have confirmed six people, including three officers, are injured in the ongoing shooting incident at the Planned Parenthood clinic, CNN reports.
Colorado Springs police say they are still encountering gunfire at the Planned Parenthood abortion clinic.
Police have said that an unknown number of civilians have been wounded after an "active gunman" fired shots at a Planned Parenthood clinic in Colorado.
Lieutenant Catherine Buckley said officers were going from building to building in the area in a hunt to treat the wounded and find the shooter, who has not yet been apprehended.
She told a mini-press conference at the scene:
- An "unknown number" of civilians have been injured
- The extent of injuries to three officers were still unclear
- Police called to the scene were met by "active gunfire"
- The shooter remains on the loose
- People caught in the area are advised to take shelter in place
Lt. Buckley said police had been called to reports of "shots fired" at the Planned Parenthood clinic at 11.38 in the morning.
She said. "When offices arrived they did encounter active gunfire. We do have three officers that are injured. We do not know the extent of their injuries."
"We have an unknown number of civilians that are injured."
She said that it was not yet possible to say whether anyone had been killed, and also refused to rule out the possibility of a second gunman.
When asked if there was a possibility that people had been taken hostage, she said: "There is that possibility, there are a lot of possibilities with this scenario."
Lt. Buckley added: "We are actively working through the different businesses and buildings to make sure that we provide medical treatment for the individuals that are injured and as well as try to locate the shooter in this situation.
"We don't have the suspect yet and we do consider this an active situation."
The search for a gunman behind a shooting at a US clinic that left at least three officers wounded remains "an active situation", a police spokesman has said.
"We don't have the suspect yet and we do consider this an active situation," Lt. Catherine Buckley told a mini-press conference at the scene, according to NBC News.
She has said the gunman's present location was unknown.
Police in Colorado Springs say there is a "possibility" that hostages were taken in the shooting attack at the Planned Parenthood clinic.