There were fears that even if unhurt, the survivors could be badly dehydrated, with daytime temperatures soaring to 35°C and about 24°C overnight.
A 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.
Clashes broke out between the relatives and police, who used batons to disperse them. Police said 50 were injured in the skirmishes.
“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 was missing.
Police say they ordered an evacuation of the building on Tuesday after cracks were found in Rana Plaza, but the factories ignored the order and were operating when it collapsed the next day.
Video footage shot before the collapse shows cracks in walls, with apparent attempts at repair. It also shows columns missing chunks of concrete and police talking to building operators.