Typhoon Mangkhut hurtled towards Hong Kong on Sunday, lashing its coastline and sending skyscrapers swaying, after killing dozens in the Philippines and ripping a swathe of destruction through its agricultural heartland.

The massive storm, considered the world's biggest this year, has already left large expanses of the Philippines' Luzon island underwater as its fierce winds ripped trees from the ground and rains unleashed dozens of landslides.

In Hong Kong, weather authorities issued the maximum alert for the storm, which rocked the city with fierce gusts that have reportedly reached 232 kilometers (145 miles) per hour.

As the storm tore past south of Hong Kong, trees were snapped in half and roads blocked, while windows and walls in tower blocks and skyscrapers were smashed.

The Philippines was just beginning to count the cost of the typhoon, but authorities have confirmed at least 25 were killed when it smashed into Luzon on Saturday.

In the northern town of Baggao, the storm collapsed houses, tore off roofs and downed power lines. Some roads were cut off by landslides and many remained submerged.

Farms across Luzon, which produces a large portion of the nation's rice and corn, were sitting under muddy floodwaters, their crops ruined just a month before harvest.

‘We're already poor and then this (storm) happened to us. We have lost hope,’ 40-year-old Mary Anne Baril, whose corn and rice crops were spoiled in the storm, told AFP.

‘We have no other means to survive,’ she said through tears.

More than 105,000 people fled their homes in the largely rural region.

- 'High threat' to Hong Kong -

An average of 20 typhoons and storms lash the Philippines each year, killing hundreds of people and leaving millions in near-perpetual poverty.

The dead included many killed in landslides, a girl who drowned and a security guard crushed by a falling wall. In addition to the 25 killed in the Philippines, a woman was swept out to sea in Taiwan.

The country's deadliest storm on record is Super Typhoon Haiyan, which left more than 7,350 people dead or missing across the central Philippines in November 2013.

Water levels in Hong Kong's famous Victoria Harbour and fishing villages could surge by up to four metres, authorities said earlier, and hundreds of residents have been evacuated to storm shelters as the observatory forecast severe flooding for low-lying areas.

Shop windows were taped up and the normally traffic-clogged streets were deserted as the storm drew nearer.

The government has warned people to stay indoors but some were strolling in the park or along the waterfront on Sunday morning.

‘I went running this morning. I love fresh air and there's no one on the streets, no cars. On normal days we can't see this,’ said Hao Chen, 28, who lives in the neighbourhood of Tin Hau, on Hong Kong Island.

Some residents reported their buildings were swaying in the wind and parks were already strewn with broken branches by the early morning.

Resident Antony Kwok in the fishing village of Tai O said flood shields and ladders had been set up to protect those who live in the area's stilt houses as waters began to rise, in a post on Facebook Live.

Almost all flights in and out of Hong Kong have been cancelled.

In the neighbouring gambling enclave of Macau, all 42 casinos shut late Saturday night and businesses were shuttered Sunday morning, some boarded up and protected by piles of sandbags.

Streets in parts of Macau were underwater as a storm surge sent water gushing from the harbour into the city.

The government and casinos are taking extra precautions after Macau was battered by Typhoon Hato last year, which left 12 dead.

Preparations were in high gear on China's southern coast, including in Yangjiang, which is not often hit by major typhoons and where the city's 2.4 million people were bracing for a direct hit.

Further down the coast preparations were also underway in Zhanjiang, where some villagers feared for the worst.

‘I couldn't sleep last night, I saw the typhoon on television and how intense it was,’ said 55-year-old Chan Yau Lok.

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