The accident occurred yesterday when the bus carrying 30 people broke the guardrail at the Baodi section of the Tianjin-Jixian expressway and fell into a ditch, a statement from the city's emergency response office said.
The driver lost control of the vehicle due to the flat tyre, it said. The four survivors, including a ticket seller and two passengers, sustained slight injuries, state-run Xinhua news agency reported.
The bus was en route to Shenyang, capital city of northeast China's Liaoning Province, from Xingtai City of north China's Hebei Province.
The bus was pulled out of the water and bodies of the victims were retrieved, the report said.