XI'AN - A blast in a public toilet in northwest China's Shaanxi Province on Saturday was triggered by excessive sewer gas in the toilet, said local authorities on Tuesday.

Investigators said that the explosion was caused by an explosive mixture of sewer gas. The toilet in Hengshan District of Yulin city collapsed in the explosion, killing one person and injuring seven others. None of the injured has life-threatening injuries.

Sewer gas consists of the products of decomposing organic waste and may include methane, ammonia and hydrogen sulphide, among many others.

Many public toilets in China, especially mid-western regions, are still dry -- basically pits exposed to the open air.

With China's fast economic and social development, local authorities have been spending heavily on renovation of sub-standard toilets, China's "toilet revolution," and sanitation has become a measure of the quality of local economic growth.