Six officers shot in Philadelphia firefight

At least six police officers have been shot in Philadelphia as a standoff between police and a shooter enters its third hour.

A firefight broke out between at least one armed gunman and police in the North Philadelphia suburb on Thursday morning, prompting a massive response from emergency services, according to local media.

At least six officers have been wounded from gunfire while two others were injured in a vehicle accident. The injuries aren't life-threatening and Philadelphia's Mayor Jim Kenney said those wounded are in good spirits.

One suspect continues to fire at police, while another - whose role in the incident is unclear - has been taken into custody. 

"Officers are attempting to communicate with the shooter; imploring him to surrender and avoid further injuries," said Sgt Eric Gripp just after 11am (NZ Time).

As of 12:50pm, the suspect remains in a residential building.

It's believed the incident began after officers went to the building for a narcotics call. Drug squad officers have been seen at the scene.

At one point two police officers were also trapped inside the building. Four women who were also inside have now been escorted out by SWAT officers.

US President Donald Trump has been briefed.

NBC was told by a woman who lives in the neighbourhood that it was "like a scene that you see in war".

"The guns, the fire, the noise, it was like bombs going off simultaneously at a time when people are having dinner".

Video from the scene shows officers crouching behind parked cars, with many aiming their firearms at the building.

A Facebook Live video by CBS Philadelphia has received thousands of views.

"We have to do something about this, I feel very sorry for our police officers," said one user.

However, Gripp has asked media to be careful with their broadcasts, as it may give away officers' tactical positions. He also said that drones should not be operated near the scene.

The local Temple University's Health Sciences Center Campus was put into lockdown, with students being asked to seek shelter and "be silent".