A June 29 traffic accident in Guangzhou, Guangdong province, that led to explosions that killed 20 people and injured 31 others was caused by an illegally parked tanker truck that was rear-ended, province officials said.

The Administration of Work Safety of Guangdong Province informed China Daily on Friday of the investigation's results.

The tanker truck's driver illegally parked the truck on the Yanjiang Expressway, while the driver of the truck behind him didn't observe the situation or take any measures to prevent the crash.

About 41 of the 54.22 metric tons of solvent oil that the tanker truck was carrying leaked and flowed down the expressway's drains to the area under the flyover along the expressway.

The volatile combustible gas from the solvent oil mixed with the air and turned into an explosive gas that was ignited by the sparks from passing vehicles under the flyover. The subsequent series of explosions burned the container yard and sheds.

The officials in charge of the accident investigation have required the local government to put on record the two drivers and people who had illegally rented out or occupied the land under the flyover, and to conduct further investigations.

The local government has taken steps to pay compensation to the families of those who died in the explosions and cover the medical fees of those injured. The families of 18 of the 20 people who died in the explosions have gotten compensation. Four out of the 31 injured have recovered and been released from the hospital.