KATHMANDU, Nepal (AP) — A passenger bus heading toward Nepal's capital veered off a key highway early Saturday, killing at least 31 people and injuring 15, officials said.

The bus drove off the highway early Saturday and plunged into the Trishuli River, which is known for fast currents, said government administrator Shyam Prasad Bhandari.

Army rescuers and divers were scouring the river searching for bodies still trapped in the wreckage, which was mostly submerged in the river.

The bodies were pulled out from the site, about 80 kilometers (50 miles) east of the capital, Kathmandu.

"We have already pulled out 31 bodies, but we believe there could be more bodies trapped in the wreckage," Bhandari said by phone from the accident site.

Bhandari, who was coordinating the rescue effort, said the river currents were making it difficult for rescuers.

It wasn't clear how many people were aboard the bus and rescuers were searching for more possible survivors despite the strong currents. Only a small section of the wreckage was visible.

Bhandari said a preliminary investigation showed that the bus was speeding along the two-lane mountain highway, which is the main route connecting Kathmandu with most other parts of the Himalayan nation.

It is a busy route, with thousands of passenger vehicles and cargo trucks plying every day.

Road accidents in Nepal, which is mostly covered with mountains, are generally blamed on poorly maintained vehicles and road conditions.