Shanghai clean-up crews yesterday ended their two-week struggle to contain China's worst ocean toxic spill. However, marine officials warned the danger posed by the release of 700 tonnes of styrene, a potentially deadly chemical when ingested, remained serious. The styrene was dumped into the East China Sea on April 17 when a South Korean freighter carrying 2,290 tonnes of the chemical collided with a Hong Kong cargo ship near the mouth of the Yangtze River. The accident took place 50km off the Shengsi Archipelago, in Zhejiang province. Afterwards, the Korean ship sailed on to an anchorage further south in the province, disregarding a marine police warning, a senior marine bureau official said. The official said a 30-square-km exclusion zone had been created around the spill area. The clean-up effort finished yesterday, successfully lifting most of the styrene from the ocean, officials said. However, they admitted some of the chemical had dissolved in the air and water and represented an ongoing threat to marine and human health. There was no immediate danger to Shanghai residents, they said. Nevertheless, scientists warned that the impact on marine life could be severe and outbreaks of cancer among people in the Shanghai area were possible. 'The spill will surely do some harm,' said an official with the Marine Bureau's hazardous materials office. 'If inhaled by humans, styrene is poisonous. If it comes into contact with the aquatic environment, marine life will be in peril.' Also unknown is the possible damage to the profitable fishing industry of the mainland's eastern seaboard. 'The losses are difficult to estimate,' said the Marine Bureau official. The 3,422-tonne South Korean freighter Dayong was travelling at high speed at 8am en route to Ningbo, in Zhejiang province, when it collided with the 46,000-tonne Hong Kong cargo ship Dawang, which was also travelling at high speed. A preliminary investigation indicated heavy fog helped cause the accident. Marine officials said their investigation was continuing.