Policemen take position beside their vehicle close to the incident site following gunmen attack on police headquarters i Karachi on Friday night. AFP

Police snipers took up positions near the station and all lights in the area were switched off.

Security forces had cleared three of the building's five floors as well as the rooftop, Murtaza Wahab, a spokesman for the Sindh provincial government, said.

The Karachi police surgeon told Reuters that two people had been killed and six wounded. A huge explosion was heard inside the station after a series of blasts when it was first attacked.

The Tehrik-e-Taliban Pakistan (TTP) took responsibility for the attack in a message sent by their spokesman to journalists.

Karachi police chief Javed Alam Odho confirmed that an attack was ongoing and said police and paramilitary troops were responding.

Earlier, TV footage showed officers surrounding the city’s central police station. Residents said they also heard the sound of explosions amid the clashes.

"Can't exactly tell how many terrorists have entered but there are at least more than five," Deputy Inspector General Irfan Baloch told Reuters.

The station houses offices of the city's most senior police. Baloch said there could have been up to 30 policemen at the station at the time of the attack.

Policemen take position near the site of an attack to a police compound in Karachi. AFP

Pakistan's Interior Minister Rana Sanaullah Khan said five or six militants were involved in the attack and threw hand grenades as they tried to force their way into the police headquarters.

Sharjeel Memon, the Sindh province's spokesman, said the attackers had been surrounded although shooting and fighting were still underway.

The TTP, separate from the Taliban ruling neighbouring Afghanistan, has recently increased attacks on police in the northwest of Pakistan as part of its campaign against the government in Islamabad.

Police sealed off traffic on the main thoroughfare through Karachi and heavy contingents of security forces, including paramilitary soldiers, had arrived at the scene.

Media reported that there were between eight and 10 assailants.

Agencies