The typhoon, which killed at least 39 in the Philippines earlier this week, was downgraded as it moved past Hainan, the Tropical Storm Risk site (www.tropicalstormrisk.com) said.
Six Vietnamese fishermen were missing near the Paracels archipelago in the South China Sea after their boat sank on Friday while seeking shelter, state-run Vietnam Television said, adding that the navy had sent rescue ships to the area.
A female tourist was also swept away by sea waves while swimming in the northern province of Thanh Hoa, the Hanoi People's Committee-run Hanoi Moi daily reported.
The city of Thanh Hoa, along with the port of Hai Phong and the neighboring Thai Binh province, lay in the path of the storm's center, state forecasters said.
The army has helped to evacuate about 150,000 people in coastal provinces while more residents will be taken from dangerous areas as the storm weakens into a low pressure system and moves further northwest.
Earlier Vietnamese riot police dispersed groups of tourists and local people who had gathered on the beaches of Haiphong to watch the high waves, state-run Voice of Vietnam reported.
On Hainan, power supplies were partially cut in Sanya, a resort city on the island's southern tip, after the first typhoon to hit China this season arrived on Friday evening.
A security guard was buried when a billboard toppled over near Sanya, and a motorcyclist died when he was clipped by another falling billboard, China's Xinhua news agency said.
The Vietnamese government warned that flash floods and landslides could strike in mountainous areas after a prolonged dry period. Vietnam Airlines said it had canceled 10 flights in and out of Hai Phong and Hanoi on Saturday.
Typhoons and tropical storms regularly hit the Philippines, China, Taiwan and Japan in the second half of the year, gathering strength from the warm waters of the Pacific Ocean or South China Sea before normally weakening over land.
