At least 36 Hindu pilgrims from Nepal were killed on Thursday when their bus plunged into a river in the mountainous northern Indian state of Uttarakhand, officials said.

The passenger bus carrying 40 people spun out of control and fell 100 feet (30 metres) into the rain-swollen Alaknanda river in Chamoli, district administrator DS Garbiyal said.

"Four survived the crash and have been hospitalised in very serious condition," Garbiyal told AFP by telephone from Chamoli, 300 kilometres (185 miles) north of state Capital Dehradun.

Police said 20 bodies had been recovered from the wreckage of the bus, which was stuck among boulders in the fast-flowing river.

Twenty-six of the victims were women, Garbiyal added.

The Nepalese, who had been touring Hindu pilgrimage sites for the past week, were returning from a popular shrine on the foothills of the Himalayas when the accident occurred, the administrator addded.

Accidents are frequent in impoverished Uttarakhand, where the mountain roads are treacherous, with many hairpin bends.