More than 40 people have died when a bus fell into a gorge in a mountainous region of northern India.

The incident on Sunday occurred in Nanidhanda area of Pauri Garhwal district in the state Uttarakhand.

"The bus lost control and swerved off the road, into a deep valley. It broke into two pieces on impact and it is now in a small river at the bottom of the valley," disaster management official Deepesh Chandra Kala told AFP news agency.

"As per official records, 45 people are dead, while many are injured," Surendra Agrawal, official at the Chief Minister's Office in Uttarakhand told Al Jazeera.

"Over 50 people were travelling in the bus," he added. "A probe will determine the reason of the accident, it could be human error or a technical snag."

India's National Disaster Relief Force (NDRF) was called to the crash site and is continuing its efforts to reach any passengers trapped in the wreckage.

The injured have been rushed to hospital.

The chief minister of the state of Uttarakhand said a "magisterial inquiry has been ordered".

Prime Minister Narendra Modi's office tweeted that Modi was "extremely saddened" by the news of the deaths.

Road accidents are frequent in India, with uncontrolled traffic junctions, badly maintained vehicles, poor driving standards blamed for most incidents.

In India, a person is killed in a road accident every four minutes, according to government data.

In April this year, 24 children and three adults were killed when a school bus plunged off a mountain road in Himachal Pradesh.

In the same month, 21 people were killed and many others suffered serious injuries after a mini-truck they were travelling in fell off a bridge over the Son river in Sidhi district of Madhya Pradesh.

"It's a combination of factors - roads are not in good condition, drivers are not trained, vehicles are not road-worthy," Harman Singh, of safety campaign group Arrive Safe, told Al Jazeera.

"New set of rules are no good unless we think of ways to ensure implementation. It was, still is and would probably remain one of the biggest challenges," he adds.

A total of 480,000 road accidents took place in India in 2016, which resulted in the loss of 150,000 lives and injured 494,000 people.

A planned law with tougher rules intended to improve one of the world's worst road-safety records is yet to pass muster through India's parliament.

About 1.2 million Indians were killed in car accidents between 2004-2014, while 5.5 million were seriously injured. (Aljazeera)