KATHMANDU (Reuters) - Rescuers in Nepal searched on Saturday for 51 passengers and crew who went missing after a landslide swept their buses into a river swollen by heavy rain, an official said, adding that the chances of finding any survivors were diminishing.

Some 500 rescuers resumed their search of the site of Friday's incident in Chitwan district, about 86 km (53 miles) west of the capital Kathmandu, but security personnel and divers have so far only found a curtain from one of the bus windows and a pair of trousers, said Khimananda Bhusal, deputy chief administrator of the district.

Seven Indian nationals are among the missing passengers. At least three other passengers managed to jump off the buses before the landslide struck, escaping with minor injuries.

"Chances of finding survivors are slim because over 30 hours have passed since the buses were swept into the river. The water level has receded this morning, but it is still very murky," Bhusal told Reuters by telephone.

Landslides and floods triggered by torrential monsoon rains have killed at least 91 people in Nepal since mid-June. Images on social media on Friday showed rescue boats on the fast-flowing Trishuli River.

Following the landslide, the government announced plans to ban buses from travelling at night in places with poor weather forecasting facilities.

(Reporting by Kathmandu newsroom; Writing by Aditya Kalra; Editing by Miral Fahmy)