At least six persons were killed and several others injured as four near-simultaneous blasts rocked the campus of a Pakistani naval training college in Lahore [Images] on Tuesday.

Plumes of smoke were billowing from the Naval War College's premises after the first two blasts that occurred almost simultaneously, witnesses said.

Two more explosions followed after a gap of few minutes.

The cause of the blasts was not immediately known, but military installations and personnel have been the target of a string of suicide attacks by the locals Islamic militants.

Over 100 people were killed in four suicide attacks in the restive North West Frontier Province in the last four days, including at a tribal council meeting and at a funeral of a slain police officer.

Six persons were killed in the blasts, television channels quoted police officials as saying.

Ambulances rushed to the War College, one of the Pakistan Navy's key training establishments, and ferried the injured to hospitals.

The War College is located close to the Mall Road, one of Lahore's main commercial areas. The institution conducts courses for senior naval officers, including those from foreign countries.

Military police and other security forces cordoned off the college and prevented journalists from going to the site of the blasts. A bomb disposal squad too rushed to the site to conduct a search.

The security forces also sealed off Mall Road as the city administration sounded an alert across Lahore.