XI'AN -- At least 36 people were killed and 13 others injured in an expressway accident in Northwest China's Shaanxi province Thursday night, authorities said Friday.

The injured are being treated in local hospitals. At least seven people are in a critical condition.

Yang Manxue, vice president of Shaanxi Sengong Hospital, told Xinhua that the hospital has received six injured passengers who are being treated by a team of experts from the top hospitals in Xi'an, the provincial capital.

Four of the six injured are in a critical condition, two sustained multiple serious injuries, while another two are undergoing operations, Yang said.

Meanwhile, Xi'an Ji Ren Hospital has received five of the injured, three of whom are being treated in the intensive care unit.

The accident occurred at 11:34 pm in the city of Ankang when a coach carrying 49 people hit the wall at the mouth of the No 1 Qinling tunnel on the Xi'an-Hanzhong section of the Beijing-Kunming Expressway, according to the State Administration of Work Safety.

The coach was en route from Chengdu, capital of Southwest China's Sichuan province, to Luoyang in Central China's Henan province.

Operated by Luoyang Transportation Group Co Ltd, the coach has a designed carrying capacity of 51 people.

The rescue work at the site of the accident finished at 6:20 am Friday. Traffic has resumed on the expressway.

The State Administration of Work Safety and the Ministry of Public Security have both dispatched work teams to oversee investigation and handling of the aftermath.