Beijing, China (CNN) -- Chinese authorities ordered beefed-up safety measures at the nation's ports after a pipeline explosion spewed crude oil into the Yellow Sea, state media reported Friday.
Ports will be required to perform checks and remove safety hazards ahead of loading, unloading or transporting oil and other hazardous chemical products, the transport ministry said in a notice on its website, according to the Xinhua news agency. China's major ports have been ordered to complete safety evaluations by the end of the year.
A state investigation has found that improper desulfurizer injections caused the oil pipeline explosion in the northeastern port city of Dalian, Xinhua said.
Two pipelines exploded July 16 at Dalian Xingang Port, causing China's biggest oil spill in recent history. Workers have been scrambling to prevent the 430-square-kilometer oil slick from further spreading into the ocean.
The blast occurred as workers were injecting desulfurizer into the pipeline after a 300,000-ton Libyan tanker had finished unloading its oil, a state investigation found, said Xinhua. The desulfurizer, used to remove impurities from crude, was strongly oxidizing, the investigation found.
The incident is still under investigation.
The accident dumped 1,500 tons of crude and caused an oil slick on the Yellow Sea that has stretched to about 430 square kilometers (165 square miles), officials have said. That is still a fraction of the 2,700 square miles of the BP spill in the Gulf of Mexico.
About 800 boats equipped with oil absorbers and dispersants have been dispatched. And crews are dumping 30 tons of oil-eating bacteria daily.
Ship traffic at Dalian, China's second-largest port for crude oil imports, was limited to avoid interference with the cleanup efforts, Xinhua has reported. And fishing, a major industry in the area, has been banned until the end of the summer.
Beijing was optimistic that the cleanup would be complete by Friday but analysts argue it may take months.
CNN's Emily Chang contributed to this report.