NANNING, May 23 -- The cause of a kindergarten bus crash, in which two kids died and 21 were injured on Friday in southwest China's Guangxi Zhuang Autonomous Region, has been identified as the vehicle being overloaded and misoperated by the driver, local authorities announced on Saturday.

The bus, which was designed to only hold 11 passengers, was carrying 24 kids and a teacher when it veered off a rural road and plunged into a pond while on its way to a small kindergarten in Guiping City on Friday morning, according to the city government.

One unharmed child was collected by his parents and 21 others were rushed to hospital.

Rain had made driving conditions unsafe and the driver failed to safely control the vehicle.

In addition, the the minibus had no school bus license and it had not been subject to an annual check, the authority said.

As of 2 a.m. Saturday, three children who were in a serious condition are showing signs of improvement. Seventeen others are in a stable condition.

The driver, a teacher and two members of the kindergarten's managerial staff are in police custody.