A large number of safety hammers in buses have disappeared in recent weeks in Zhengzhou, in Central China's Henan province.

The hammers were likely stolen by drivers, who put the hammers in their own vehicles for emergency use, said Song Yufeng, a manager at the Zhengzhou Bus Communication Corp.

She added that on August 1 as many as 30 hammers on the company's buses had disappeared in the past week.

The rising number of safety hammer theft cases follows a case in which a driver died after failing to escape from a car and died after the vehicle became waterlogged under the Guangqumen Bridge in Beijing on July 21.

The man tried to break the car's window with his fist but his efforts were futile, according to a report in caixin.com.

"The weather forecast said that it's going to rain in Zhengzhou in the following days, and some drivers have started to prepare for emergency cases," she said.

A middle-aged woman was caught stealing a safety hammer on a bus in Zhengzhou on July 27, said Li Chao, the bus' 37-year-old driver.

Li and the passengers found three more hammers in her bag afterward. She said that she was going to give the hammers to her children so that they could play.

To prevent the safety hammers from being stolen, the bus company had to install alarms. The alarms will go off if passengers touch the hammers.

The number of safety hammer sales on online store taobao.com increased nearly 600 percent two days after the man died, and the number of flashlights and lifejackets sold increased nearly 20 times.

Liu Hua contributed to this story.