Crews bored deeper Friday into the wreckage of a garment-factory building that collapsed two days earlier, hoping for miracle rescues that would prevent the death toll from rising much higher, as angry relatives of the missing clashed with police.

Some of those trapped under fallen concrete in the Rana Plaza building were still alive, rescue workers said, but they were so badly hurt and weakened that they will need to be extricated within a few hours if they are to survive.

Brig. Gen. Mohammed Siddiqul Alam Shikder, who is overseeing rescue operations, said the death toll at the Rana Plaza building had reached 290, and that 2,200 people have been rescued. The garment manufacturers' group said the factories in the building employed 3,122 workers, but it was not clear how many were inside it when it collapsed Wednesday.

Hundreds of rescuers, some crawling through the maze of rubble, spent a third day working amid the cries of the trapped and the wails of workers' relatives gathered outside the building, which housed numerous garment factories and a handful of other companies.

Police cordoned off the building site, pushing back thousands of bystanders and relatives, after rescue workers said the crowds were hampering their work.

Clashes erupted between relatives of those still trapped and police officers, who used batons to disperse the mobs. Police said 50 people were injured in the clashes.

"We want to go inside the building and find our people now. They will die if we don't find them soon," said Shahinur Rahman, whose mother is missing.

An army rescue worker, Maj. Abdul Latis, said he found one survivor still trapped under concrete slabs, surrounded by several bodies. At another place in the building, four survivors were found pinned under the debris, a fire official said.

The rescue workers said they were proceeding very cautiously inside the crumbling building, using their hands, hammers and shovels, to avoid more injuries to trapped survivors and avoid further collapses.

Police say cracks in the building had led them to order an evacuation of the building the day before it fell, but the factories ignored the order.

A military official, Maj. Gen. Chowdhury Hasan Suhrawardy, told reporters that search and rescue operations would continue until at least Saturday.

"We know a human being can survive for up to 72 hours in this situation. So our efforts will continue non-stop," he said.

Some people have been pulled out of the wreckage alive, though severely weakened, more than a day after the collapse.