Super Typhoon Usagi, the most powerful storm of the year, brought torrential rain and ferocious winds to Taiwan Saturday, leaving tens of thousands without power and throwing travel plans into disarray as it barrelled towards Hong Kong.

Southern Taiwan was battered by the storm, which rolled past the Batanes island group in the far north of the Philippines overnight -- tearing coconut trees in half -- and headed on towards the Chinese mainland.

By 1100 GMT Usagi was 610 kilometres (400 miles) southeast of Hong Kong, forcing local carrier Cathay Pacific to warn that all its flights in and out of the city will be cancelled from 6:00 pm (1000 GMT) on Sunday.

Usagi was packing maximum sustained winds of up to 195 kilometres per hour, the Hong Kong Observatory said, as people in the city reinforced windows in anticipation of the approaching storm's impact.

In Taiwan's southern Pintung county, storms flooded remote villages, forcing troops to evacuate dozens of people, the state Central News Agency said.

"I thought a tsunami was hitting... I've never encountered this before in my life," it quoted as saying a 60-year-old woman who was scrambling to safety with her pet.

Six people were injured in Kinmen, a Taiwan-controlled island off China's southeastern Fujian province, after they were hit by fallen trees, according to the Central Emergency Operation Centre.

The typhoon also left 45,000 homes powerless and more than 5,000 households without water, it said. Pictures showed overturned vehicles, fallen branches and rivers of muddy water flooding the streets.

A total of 77 domestic and five international flights were cancelled and ferry services suspended, with schools and offices in many parts of Taiwan closed, especially in the south and east, authorities said.

The defence ministry deployed more than 3,000 soldiers to "high-risk" areas and placed 24,000 others on standby.

Nearly 3,000 people had already been evacuated, officials said, as the Central Weather Bureau warned people to expect up to 1.2 metres (47 inches) of rain.

In the Philippines' Batanes island chain terrified locals spent the night in their houses as savage winds raged outside.

"This is the strongest typhoon to hit Batanes in 25 years," Dina Abad, the district's representative to Congress, told AFP.

"The howling winds began at midnight and they churned up to eight-metre waves that damaged the port and sank moored fishing boats," she said, quoting a mayor of one coastal town.

She said coconut trees were torn in half or were uprooted, while terrified residents couldn't sleep as the storm battered roofs above their heads. The aviation tower at the island's airport was also badly damaged.

"I think the estimate of the damage will be bigger tomorrow when have a clearer assessment on the ground," she said.

In Hong Kong, officials issued a standby signal number one, the first in a five-step tropical cyclone warning system with winds expected to strengthen later Saturday and on Sunday.

"It is anticipated that disruptions will continue on 23 September, Monday," flag carrier Cathay Pacific said in a statement.

Operators at the city's port, one of the busiest in the world, said they would cease work late Saturday.

China's National Meteorological Center issued a red alert -- its highest-level warning -- as it forecast gale-force winds and heavy rain.

It said Usagi would affect the coastal areas of the provinces of Guangdong, Zhejiang and Fujian as it moved northwest.

Nearly 23,000 fishing boats had earlier taken shelter in Fujian province ahead of the storm, state media reported, while more than 4,000 people living in coastal areas were evacuated.

The region is regularly pummelled by tropical storms. Typhoon Bopha left a trail of destruction in the southern Philippines last year, triggering floods and landslides that left more than 1,800 dead and missing and displaced nearly one million people.

In August 2009, Typhoon Morakot killed about 600 people in Taiwan, most of them buried in huge landslides in the south, in one of the worst natural disasters to hit the island in recent years.

Hong Kong rarely suffers major loss of life as a result of tropical storms, although Typhoon Rose in 1971 killed 110 people in the city.