Several Chinese fishermen are missing after their boats capsized as Typhoon Bolaven hit South Korea.
The boats were just off Jeju island when they went down, South Korean media said. Six people were rescued but several more are thought to be missing.
Power has been cut to tens of thousands of homes and trees have been felled. The typhoon is expected to move north, passing Incheon port later in the day.
Many flights have been cancelled and all schools in the capital closed.
Typhoon Bolaven is also bringing strong waves and rain to China’s north and east coasts, reports said.
It has already lashed the Japanese island of Okinawa, causing power cuts and paralysing transport.
High winds, torrential rain and property damage were reported on Jeju island as the typhoon hit.
A spokesman for the coastguard told AFP news agency that six people had been rescued from the two Chinese ships, one of which had sunk completely.
It is not clear how many people were on the two boats. Those rescued put numbers between 31 and 34, AFP said.
All schools in Seoul and most others across the country have closed for the day, Yonhap news agency reported.
US and South Korean forces have halted a major joint exercise that had started last week.
Meanwhile, China has issued a yellow alert – the second-highest level – as forecasters expect Bolaven to make landfall in Dandong in the north-eastern Liaoning province and north-western North Korea on Tuesday, China’s state Xinhua news agency reported.
On Sunday the typhoon hit the Japanese islands of Okinawa and Kagoshima, leaving some 75,000 households without power. At least four people were injured.
The latest typhoon is the 15th destructive storm of the season in East Asia.
Bolaven comes just after Typhoon Tembin, which has caused widespread damage in Taiwan.
On Monday night, Taiwan was bracing for Tembin to hit the same southern region where it unleashed more than 50cm (20 inches) of rain within 24 hours several days ago.
But early on Tuesday the typhoon appeared to have passed off the southern coast, without making landfall.
BBC © 2012