BEIJING/TAIPEI - Typhoon Saomai gathered strength as it swirled towards Chinese mainland, with landfall expected on Thursday, while a tropical storm fizzled to the south of Taiwan and another veered towards the east of Japan.

At 0900 GMT, Saomai was 630 km (390 miles) southeast of the Chinese coastal city of Wenzhou in Zhejiang province and moving northwest at 25 kph, meaning Taiwan was likely to escape the brunt of the storm, China's Central Meteorological Office said.

Heavy rains will hit Zhejiang and the neighbouring province of Fujian through Friday, with wind gusts of 70 to 120 kph, Xinhua news agency said.

Authorities have warned of floods and landslides in mountainous areas and advised all ships to return to harbour by Wednesday evening.

Much of south China has been repeately battered by typhoons and tropical storms this year, with hundreds of people killed by rainstorms, mudslides and floods.

Tropical storm Bilis killed more than 600 lives alone last month and Typhoon Prapiroon killed about 80 last week.

Taiwan's weather bureau issued land and sea warnings, anticipating strong winds in northern Taiwan. Keelung, Taiwan's second largest port, may have to close, a port official said.

Typhoons and tropical storms are common in Taiwan, southeast Chinese mainland and the Philippines during a season that lasts from early summer to late autumn. They gather strength over the warm water and tend to weaken once they make landfall.

On Tuesday night, tropical storm Bopha passed over southern Taiwan with little impact, except that a few domestic flights were cancelled in the island's southeast.

A third tropical storm, Maria, veered away from Japan's main island of Honshu and was moving northeast at the speed of 35 kph (22 mph) on Wednesday.

But the storm could dump as much as 15 cm (6 inches) of rain in some coastal areas north of Tokyo, weather forecasters warned.