A crowded bridge collapsed amid heavy rains in northwestern Pakistan on Saturday, flinging pedestrians and cars into a flooded stream, killing at least 39 people and injuring three, an official said.

Witnesses said about 200 people and some vehicles were on the 30-foot-high bridge in the city of Mardan when it suddenly collapsed, apparently due to the torrent of water rushing beneath.

Rescuers have pulled 39 bodies from the rubble of the bridge and the floodwater, but they don't expect to find many more, said Ibrahim Buland, a deputy mayor, adding that there was still some rubble to be removed.

Abdul Wail Khan Yusafzai, the liaison officer of the Flood Warning Center, said that although the bridge was old and overcrowded, it mainly collapsed because of the floodwater.

Rescue efforts in Mardan, about 60 miles northwest of the capital Islamabad, were hampered by the darkness as night fell.

Ehtisham Khan, a rescue worker at the scene, told The Associated Press that three vehicles were buried under the collapsed bridge with bodies inside. The army and local authorities used floodlights to help the rescuers.

Hundreds of curious onlookers gathered at the site.

Umair Ali, 23, a college student who lives nearby, estimated there were between 150 and 200 people on the bridge when it collapsed.

"I saw some of them swimming and coming out of the water," he said, adding that dozens more could be under the debris.

Abid Ali, the city police chief, said they needed heavy machinery and tools to cut through steel and concrete debris.

Another police official Mohammed Iftikhar said others may have drowned in the swollen stream.

Dozens of people have died across Pakistan in recent weeks due to monsoon rains, landslides and flash floods. The rains have forced authorities to open the spillway to a major dam near Islamabad for the first time in five years.