NANJING - The death toll from a gas leak at a steel plant in East China's Jiangsu province Thursday has risen to six as three critically injured workers died Friday, local authorities said.

The accident occurred on Thursday noon at Meishan Steel Plant in Nanjing, capital of Jiangsu, when gas leaked from a pipeline into a gas tank under repair by 13 technical workers.

Besides the six deaths, the other seven workers are still being treated at a hospital and are in stable conditions, the Nanjing municipal publicity department said in a statement.

The cause of the accident is still under investigation.

Meishan Steel Plant belongs to Baosteel Group, a state-owned steel giant based in Shanghai. The plant outsourced equipment maintenance work to the Nanjing branch of Baoye Construction Corporation, where the workers are from.