Dozens of boats worked Thursday to clean up a massive oil spill in the South China Sea (search) caused by a collision between two container ships, after divers were sent to patch the hull of the leaking vessel, state television reported.

Earlier reports said the spill was China's worst in five years.

The oil tank on the German-registered MSC Ilona (search) was punctured during a collision Tuesday night with the Panama-registered Hyundai Advance near the mouth of the Pearl River, northwest of Hong Kong. No injuries were reported.

On Thursday, 17 specialized anti-pollution boats and 35 fishing boats struggled to clear the spill, which had lengthened from 10 miles to 14 miles long, China Central Television reported.

Officials with the Maritime Bureau of the Ministry of Communications warned ships to steer clear of the area, the report said.

On Wednesday, divers were sent to patch the MSC Ilona's hull, the official Xinhua News Agency reported.

The MSC Ilona was sailing from Shanghai to the southern Chinese city of Shenzhen, which abuts Hong Kong, when the accident occurred, Xinhua said. The Hyundai Advance was departing Shenzhen for Singapore.

Earlier reports suggested the MSC Ilona was an oil tanker, but it was later identified as a container ship.

It was not clear what cargo the two ships were carrying.