Emergency workers continued to search for survivors in the smoldering remains of the Marriot Hotel in Islamabad, Pakistan, one day after a massive truck bomb shattered the hotel and killed at least 53 people.

The lavish hotel was a favorite for foreigners and the Pakistani elite. Among the dead was Czech Ambassador Ivo Zdarek and at least one member of the U.S. military.

Security officials say that some parts of the ruins are still so hot that some bodies cannot be recovered. There are also worries that what is left of the building could collapse.

"The building's structure is dangerous," Malik Ashraf Awan, a senior civil defense officer, told The Associated Press. "It consumed too much heat and shock."

Security footage of the attack has been released, showing the moments leading up the explosion. The tape shows a dump truck ramming the security barrier, causing guards to scatter. They nervously return to investigate the truck, when a small explosion rips through its cab.

One guard tries to put out the fire, but they did know that the back of the dump truck was filled with nearly 600 kilograms of explosives.

Investigators have made a disturbing discovery about the explosives. Initial reports suggest it may have been fertilizer, normally used in terrorist attacks, but officials now believe it may have been military-grade material.

The tape does not show the massive explosion that left a 10-metre crater and destroyed much of the hotel. At least 250 people were wounded.

The attack at about 8 p.m. local time Saturday, just when Muslims were breaking the Ramadan fast and hotel restaurants were packed with diners.

The explosion came just hours after President Asif Ali Zardari made his first address to Parliament. Rehman Malik, the head of Pakistan's Interior Ministry, told The Associated Press that officials had received intelligence suggesting there might be some kind of militant activity because of Zardari's address.

Following the attack, Zardari appeared on national television to express his condolences to the victims and promised to expel the "cancer" of terrorism from Pakistan.

With files from The Associated Press