The coach crashed in Qinling tunnel in Shaanxi province on Thursday night, according to Xinhua news agency, which cited local authorities.
The bus had departed from Chengdu in southwest Sichuan province en route to the central city of Luoyang.
The injured have been rushed to hospital, Xinhua said. According to Sina news website, the bus had a 51-passenger capacity and was carrying 49 people, including two children.
Sichuan province is already reeling from another tragedy as 20 people were killed and hundreds more injured in an earthquake that struck the region on Tuesday night.
Deadly road accidents are common in China, where traffic regulations are often flouted or go unenforced by police.
The country's frequently overcrowded long-distance buses are particularly prone to fatalities.
There were more than 180,000 traffic accidents and 58,000 deaths in 2015, authorities said in December.
Traffic law violations caused almost 90 percent of the road accidents where people died or were injured in 2015, with the total number of such infractions reaching an astonishing 442 million.
Last month, 11 people died and nine were injured when a bus carrying 19 people collided with a lorry on a national highway in northern Hebei province.
Ten people were killed and 38 injured in March when a bus collided with a cement truck in the southwestern province of Yunnan.
At least 18 people were killed when a minibus plunged into a lake in the central city of Wuhan in December.
Last November, a pile-up on an expressway in the northern province of Shanxi killed 17 people and damaged 56 vehicles.
And in July last year, a coach crashed through a highway guard rail and plunged into a canal near the northern city of Tianjin, killing 26.
Share
