KATHMANDU, Dec 12 (Reuters) - A school bus crashed in southwest Nepal, killing at least 22 people, most of them children returning from a picnic, police said on Friday.

The bus skidded off a bridge on a highway and plunged 30 metres (100 feet) in Nawalparasi district, about 150 km (93 miles) southwest of Kathmandu late on Thursday.

"At least 52 others were injured and are undergoing treatment at a medical college and nearby hospitals," Chet Bahadur Khatri, an officer at the Nawalparasi police control room said.

The cause of the accident was not known.

Accidents are common in mostly mountainous Nepal where roads are poorly maintained. (Reporting by Gopal Sharma; Editing by Alistair Scrutton and Sanjeev Miglani)

(For the latest Reuters news on Nepal see: http://in.reuters.com, for blogs see http://blogs.reuters.com/in/)

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