Savar, Bangladesh ? A nine-story garment factory in Bangladesh collapsed after a boiler exploded Monday, killing at least 21 people and trapping about 200 others, police and rescuers said.

Rescuers used welding machines to cut holes in the rubble to reach people and pump air to survivors at the sweater-making factory near Savar, an industrial town 20 miles northwest of the capital Dhaka.

Police said at least 300 people were in the factory when it collapsed. Twenty-one bodies have so far been recovered and nearly 200 people are believed to be still beneath the rubble, said Selim Newaz Bhuiyan, a fire brigade official at the scene.

At least 92 injured workers were pulled from the debris and taken to hospitals, he said.

Anxious relatives joined soldiers and firefighters in using bare hands and crowbars to remove rubble. They said narrow roads leading to the collapse site had restricted access for cranes and other rescue equipment.

At one point, a trapped worker called relatives on his cell phone from beneath the slabs of concrete.

“He said he was dying and he asked for some water,” said Nurul Islam, a police official supervising the rescue effort. “We are trying to locate him.”

One manager at the factory said he plunged from the seventh floor in a jumble of concrete.

“I was overseeing the workers when there was a big bang and (the) building suddenly started shaking and going down,” said Helaluddin, who uses one name.

Rescue workers try to retrieve several hundred workers who were trapped after a nine-story building collapsed following a boiler explosion Monday morning west of Dhaka, Bangladesh.

“I was buried under slabs of concrete before I could realize what had happened,” he said before being taken to a hospital.

There were fewer women in the factory than earlier believed because male workers are preferred for the late-night shift, survivor Haider Ali said. Officials initially said most of the victims were women.

The government has ordered an investigation into the accident, Junior Home Minister Lutfozzaman Babar said after visiting the site.

The collapsed factory was built on a swamp three years ago, workers said.

The factory, Spectrum Garments, produced nearly 80,000 pieces of clothing for export annually, mainly to the United States, Belgium and Germany, employee Kaiser Ahmed said. But he could not specify the brand names of the products.

Bangladesh has about 2,500 garment factories employing about 1.8 million workers — about 90 percent of them women.

The South Asian nation exports more than $5 billion in textiles each year.