NINGBO - An unknown amount of oil is leaking into the Yongjiang River in the coastal city of Ningbo in East China's Zhejiang province after an oil tanker explosion that killed at least seven people on Saturday morning.

Six ships are dealing with the oil leak at the scene, according to the provincial maritime affairs bureau.

In addition to the confirmed deaths, one person was injured when the oil tanker exploded and caught fire at about 8:40 am at Zhangjianqi shipyard in Ningbo's Zhenhai District.

The accident happened when the 300-tonne vessel was being repaired.

The blaze was extinguished at about 11 am, and the cause of the accident is under investigation.

The 130.96-km-long Yongjiang River is a major water source for the booming city of Ningbo, which has a population of more than 7 million.