At least 30 people were killed on Sunday when an overcrowded bus plunged off a mountain road into a gorge in northern India, officials said.

Chief Minister of Uttarakhand state Trivendra Rawat said the bus fell into a 700-foot (213-meter) deep gorge in the Himalayan foothills. He said about a dozen others were injured, some of them critically.

Rescue and retrieval work was hampered by inclement weather, said senior police official Sanjay Gunjiyal. He said rescuers have so far pulled out 20 bodies.

Police said the 28-seater bus was carrying about 45 daily commuters.

It wasn't clear what caused the crash. But Gunjiyal said bad weather could have led the bus to skid off the road. “It is raining (in the area) since morning.

Two days back there was a landslide in that area,” he said, adding that residents were the first to reach the site and help the victims.

Gunjiya said the terrain was inhospitable and communications poor.

“Three choppers are waiting for clearance. If weather permits, these will be pressed into service to evacuate the injured” to the state's capital Dehradun, he said.

India has the world's deadliest roads, with more than 110,000 people killed annually. Most crashes are blamed on reckless driving, poorly maintained roads and ageing vehicles.