Five people were killed and three others remain missing after a vehicle-mounted testing apparatus exploded Sunday in an oil extraction plant in northwest China's Shaanxi Province, local authorities said Monday.

The accident happened at 7 p.m. when the vehicle returned from an oil well in Qilicun oil extraction plant of Yanchang Oil Field Co., Ltd. in Yanchang County in the city of Yan'an, which boasts rich oil and gas resources.

The vehicle, which conducted tests at the plant, belongs to a thermal power technology company from central China's Hunan Province.

Five other people injured in the blast are being treated in hospital and are in stable condition now.

Rescuers are searching for the missing. The cause of the blast is under investigation.