At least 30 people were killed and 37 injured when a bus plunged off a road in India's hilly northern state of Himachal Pradesh on Thursday, a government official said.

"About 60 to 65 people were on board the bus," said Akshay Sood, a senior civil servant in Kullu district, where the accident took place.

"Relief and rescue are still going on, and the number (of dead) may rise."

Indian roads are among the world's deadliest, with nearly 148,000 people killed in more than 460,000 accidents in 2017, according to government data.

Prime Minister Narendra Modi expressed his dismay over the accident.

"Deeply saddened by the bus accident in Kullu. Condolences to the families of those who lost their lives. I hope the injured recover soon," Modi's office said in a tweet.