|Muifa triggered heavy rains in Shanghai as it passed by the megalopolis [Reuters]
Tropical storm Muifa has battered northeastern China and parts of the Korean peninsula.
The storm battering the northeast Chinese coast on Monday whipped up waves that threatened a dyke protecting a chemical plant, news media reported.
At least four people were killed and two others were missing in western South Korea due to torrential rain and heavy winds, the Yonhap news agency reported.
Large waves were also generated by the tropical storm, which China's weather agency said made landfall late on Monday afternoon in North Korea.
North Korea's official Korean Central News Agency said heavy rain was expected through the night in northwestern provinces as the storm moved northward.
South Korea's state weather agency, the Korea Meteorological Administration, said up to 200mm of rain were expected in some western areas of North Korea, along with waves up to 8m high along coastal areas, the agency said.
Previously classified as a strong typhoon, Muifa downed power lines, billboards and trees in Shanghai and brought heavy rain to coastal Shandong province on Sunday.
The US embassy had urged Americans in the area to "take all necessary precautions".
Last week, Muifa killed four people in the Philippines and caused injuries and power outages in far southern Japan without making landfall.
Averting toxic disaster
Waves as high as 20m broke the dyke in China's Liaoning province and threatened to hit the compound of the Fujiahua chemical plant where unspecified chemicals were held, and residents were told to evacuate, the Xinhua news agency said, citing soldiers at the scene.
Workers scrambled to protect the facility after waves breached the plant's coastal defences.
An official from Dalian's Propaganda Department referred to two reports on a Dalian news website that said the danger had been controlled and the dyke was being reinforced with large stones and concrete.
Soldiers and workers with forklift trucks were involved in the effort to prevent sea water from creating a spill of toxic chemicals from the plant, the report said.
Authorities did not say which chemicals had been in danger of spilling from the plant, which makes paraxylene - a flammable, carcinogenic liquid used in the production of polyester films and fabrics.
A serious chemical leakage would have been a fresh headache for Liaoning, which recently suffered an oil spill from two offshore platforms.
Pollutants from that spill have been found spreading to beaches, and been blamed for losses to tourism and aquatic farming businesses, Xinhua reported in July.
Tens of thousands of people living along China's east coast were evacuated over the weekend as Muifa approached, amid fears it would hit Shanghai, the country's densely populated commercial capital.
Chinese airlines cancelled hundreds of flights and thousands of fishing boats were ordered to stay in port.
But the city was spared a direct hit, suffering only some power outages and minor damage as the storm passed by.