GUANGZHOU - Overload protection failure is to blame for a Friday's elevator plunge that injured 20 in south China's Guangdong Province, local officials said Saturday.

An initial investigation has indicated that the overloading then led to the failure of the bake system of the elevator in an office building in the city of Dongguan, sources with the Nancheng District government said.

The elevator with 21 people ran down from the 19th floor to the 7th floor in midnight Friday and shortly stopped before it plunged to the basement floor.

Twenty people inside were injured with fractures or bruises. Twelve of them were hospitalized instantly while the eight others were sent back home for self treatment.

As of 5 pm Saturday, six people remained in hospital for further observation and treatment, but none of them are in serious conditions.

The elevator is manufactured by Hangzhou-based Xizi Otis Elevator Co., Ltd., a joint venture between Otis Elevator Company and China's Xizi Elevators Group.

The elevator was put into use in 2005, with a rated load of 1000 kg or 13 people.

However, a total of 21 people, including 14 men and seven women, were in the elevator when the accident occurred, according to the sources.