At least 59 people have been killed in an attack on a police academy in Pakistan, officials say.

Gunmen stormed the training college in Quetta, the provincial capital of Baluchistan, opening fire and detonating explosives.

More than 100 others have been injured, some of them critically.

Between four and six gunmen raided the training centre, attacking a dormitory where up to 250 police trainees were resting.

"They were rushing toward our building firing shots so we rushed for safety toward the roof and jumped down in the back to save our lives," one of the trainees told Pakistan's Geo television.

Pakistani police and paramilitary forces exchanged fire with the gunmen for several hours after the attack amid reports that a number of trainees were taken hostage.

At least one of the attackers was killed in the counter-terror operation and two detonated their explosive vests, according to Baluchistan Home Minister Sarfaraz Bugti.

He said security forces have now completed their operation, but are still engaged in the clean-up process.

No one has claimed responsibility for the attack.

It came hours after gunmen shot and killed two customs officers and wounded a third near the town of Surab, about 90 miles south of Baluchistan's provincial capital Quetta.

Baloch separatist groups in Baluchistan have claimed similar hit-and-run attacks on security forces and government officials in the past.

Islamic militants also have a presence in the province, which borders Afghanistan.