Authorities finished the rescue work of freeing people Tuesday morning from a bus wreck in a ravine of south China's Guangxi Zhuang Autonomous Region, 20 hours after the accident that killed seven people and injured 50.

The bus, en route from Dongguan, a manufacturing town in the booming Guangdong Province to Luzhou City in the southwestern Sichuan Province, veered off the highway and plunged into a 100-meter deep ravine in Hechi City after colliding with a sports utility vehicle at 2 p.m. Monday.

Most of the passengers on the bus were migrant workers who were going home for the Chinese Lunar New Year that falls on Sunday.

Qu Bin, a passenger who survived with slight injuries, said he could only travel by bus because he had lost his ID card and was unable to board a train or plane. "I was with my elder brother Qu Bo and we both ended up getting injured."

Police in Hechi City said the bus, carrying 53 people, was owned by a travel service based in Zunhua City of the northern Hebei Province.

Authorities are investigating whether the bus service was legal, as a document found in the wreckage indicated the bus had been contracted to a construction firm based in Chongqing Municipality from Feb. 5 to 11 and was supposed to travel from Tangshan City in Hebei to Chongqing.

"I boarded the bus in Dongguan and knew nothing about the Chongqing firm," said Qu.

Qu said he and his brother got on the bus from Tangxia town in Dongguan at 9 p.m. Sunday. They paid 680 yuan (100 U.S. dollars) each for the bus fare, but were not given any ticket.