SHANGHAI, CHINA - THE algae plaguing China's Olympic sailing venue is spreading to other ports and beaches along the coast, state media has reported, despite official claims that the battle is being won.

Officials in Jiangsu province activated an emergency plan on Friday, assigning experts on marine patrol ships and two helicopters to stop the spread of algae that has appeared in the state's Yellow sea waters, Xinhua reported.

At the end of June officials said the weeds had affected a total sea area of 13,000 square kilometres, but it has continued to grow offshore even as cleanup efforts closer to shore have been stepped up.

Chinese officials are also facing trouble on another front as swarms of locusts that left thousands of hectares barren in Inner Mongolia, threaten to descend on Beijing, the Beifang Xin Bao reported this week.

Jiangsu borders Shandong province where the algae bloom first appeared in late May. Qingdao, Shandong's major resort city, is hosting the Olympic sailing competition next month.

Officials in Jiangsu' Lian Yungang and Shandong's Ri Zhao have jointly set an algae task force and China's State Ocean Administration has also stepped up monitoring of waters neighboring Shandong, Xinhua reported on Friday.

Environmentalists say the algae is caused by sewage and agricultural waste.

But government officials have played down links to pollution, saying this year's unusually large bloom is due to heavy rain and hot weather.

China has invested heavily in cleaning up the water around Qingdao, including moving sewage discharge pipelines away from the shore and out to sea.

Qingdao officials have set a Tuesday deadline to clean up all the algae from the city's waters and have drafted more than 10,000 soldiers and volunteers and hundreds for fishing boats to help.

A barrier more than 22 kilometres long of constructed out of inflatable oil booms and was completed on Saturday sealing off sailing courses from invading algae, Mr Qu Chun, the Olympic sailing competitions manager said.

'From what we see today after finishing an inspection tour, there is very little algae on the courses, which shows our previous efforts worked', Mr Qu told AFP on Saturday.

The algae has spread as far as the county of Rongcheng, about 200 kilometres up the coast from Qingdao, near the northern tip of China's Yellow Sea Coast.

Authorities in the coastal counties of Rushan, Wendang and Wengcheng were also forced to mount cleanup efforts in the midst the summer tourist period, state press reported.