A bus rolled over on one of the longest cross-sea bridges in the world on Monday, killing six people and injuring 43 others, Chinese state media and the bridge's management said.

It was not immediately clear what caused the one-vehicle accident, said Li Hailiang, an employee at the Donghai Bridge Administration in the eastern Chinese city of Shanghai.

He said six people died on the scene. Another 43 were injured when the 55-seat bus overturned, according to the official Xinhua News Agency, citing the Shanghai municipal government.

Donghai Bridge connects Shanghai, China's financial metropolis, with a deep-water port in the East China Sea. With a length of 32.5 kilometers (20.2 miles), it is one of the longest cross-sea bridges in the world.