Ragasa had already toppled trees, torn the roofs off buildings and killed at least two people while ripping through the northern Philippines, where thousands sought shelter in schools and evacuation centres.

The super typhoon was generating maximum sustained winds of 195 kilometres (121 miles) per hour near its centre while moving west across the South China Sea, according to Hong Kong's weather service.

The Hong Kong Observatory issued its highest typhoon warning, T10, at 2:40 am (1840 GMT Tuesday), saying it will "remain in force for some time" as Ragasa comes closest to the Chinese finance hub later in the morning.

It also warned of significant swells and storm surge as the storm moves through, with some areas potentially seeing water levels four to five metres above normal.

An AFP reporter saw waves nearly five metres high smash into the seaside promenade of Hong Kong's Heng Fa Chuen residential district around nightfall.

Resident Terence Choi said he had stocked two days' worth of food at home, adding that he was "quite nervous" about the prospect of the housing estate losing power and fresh water supply.

Yang Lee-o, who has lived in the coastal neighbourhood of Lei Yue Mun for 40 years, said government workers had already spent a day placing sandbags.

"Lei Yue Mun is the hardest hit whenever there's a typhoon or rainstorm," said the 71-year-old, adding that the water level went up to her thighs during a previous super typhoon.

Hong Kong's number-two official, Eric Chan, previously said Ragasa would pose a "serious threat" comparable to the super typhoons of 2017 and 2018, which cost hundreds of millions in property damage.

Scientists warn that storms are becoming more powerful as the world warms due to the effects of human-driven climate change.

- Southern China affected -

Ragasa -- named after the Filipino word for rapid motion -- is expected to make landfall in the central and western coastal areas of Guangdong within 24 hours, the province's emergency management bureau said on Tuesday morning.

At a commercial street across from the main train station in the southern city of Zhuhai on Tuesday afternoon, locals were preparing storefronts for the approaching storm.

Among them was 28-year-old Hong Wei, who spoke to AFP while placing long strips of tape across the glass windows of a shop.

"This typhoon is quite powerful," said Hong. "So we put some safety tape on the glass to prevent it from breaking up into many small pieces and flying around," he said.

"We're trying our best to avoid some safety issues... I'm quite worried."

Nearby, workers at a tea shop piled outdoor furniture inside, while other businesses had shut early in anticipation of the storm.

But many locals in the typhoon-prone region told AFP that they weren't too concerned about the reports, with one 20-year-old man in Zhuhai surnamed Huang telling AFP he was "used to it".

Huang said he still planned to take precautions: "I'll stick some tape on my windows and stock up on various things. That's very important."

Shenzhen earlier ordered the evacuation of 400,000 people.

Emergency management authorities in the Chinese tech hub said that except for emergency rescue personnel and those ensuring people's livelihood, "do not go out casually".

Other cities in the southern province of Guangdong that are implementing the measures include Chaozhou, Zhuhai, Dongguan and Foshan.

In Hong Kong, classes were to be suspended on Tuesday and Wednesday, though the stock exchange adopted new rules this year to keep markets open during typhoons.

There were no flights out of Hong Kong after 1000 GMT, according to the airport's website. Cathay Pacific earlier said that more than 500 of its flights were set to be cancelled.

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CATHAY PACIFIC AIRWAYS