LANZHOU - A traffic accident early Friday morning in an expressway tunnel in Northwest China's Gansu province caused two tank trucks to blast. Casualties were unknown.

Related readings:  5 killed, 30 injured in bus stand blast in NW Pakistan  5 dead in east China factory blast  110 killed in Yemen bullet factory blast  Coal mine owner in custody after blast kills 11

The blast that occurred at around 3:50 am badly damaged the tunnel facilities and led to the closure of the expressway linking Gansu's capital city of Lanzhou and Linxia Hui autonomous prefecture, according to the provincial expressway operation management center.

The accident also involved a cargo truck. No further details of the accident were available.

Firemen were still working to put out the fire.