Ragasa was generating winds with maximum sustained speeds of 220 kilometres per hour (137 miles per hour) at its centre as it churned across the South China Sea early Tuesday, having earlier lashed parts of the Philippines, according to Hong Kong's weather service.

The finance centre was preparing for extensive disruption and damage, while nearby Chinese tech hub Shenzhen has ordered the evacuation of 400,000 people.

"Ragasa will pose a serious threat to Hong Kong, which could reach the levels of Hato in 2017 and Mangkhut in 2018," Hong Kong's number-two official Eric Chan said on Monday -- referring to two super typhoons that each cost hundreds of millions in property damage.

Hong Kong's airport will remain open but there will be "significant disruption to flight operations" from 6:00 pm (1000 GMT) Tuesday until the next day, the Airport Authority said.

More than 500 Cathay Pacific flights are expected to be cancelled.

Hong Kong Observatory said it would issue its third-highest typhoon warning, T8, at 2:20 pm (0620 GMT) on Tuesday, at which point businesses close up and most transport shuts down.

- 'Better precautions' -

Residents scrambled to stock up ahead of Ragasa's arrival, leaving supermarket shelves empty of fresh food, vegetables and bread.

"There's bound to be some concern," said supermarket shopper Zhu Yifan, a 22-year-old student from China.

Zoe Chan, in her fifties, piled up sandbags outside her clothes shop in the Wanchai district, saying she expected her business to be "ruined" by water damage.

"The most important thing is to take better precautions, so I can rest easier," Chan told AFP.

School classes will be suspended on Tuesday and Wednesday. The Hong Kong Jockey Club also cancelled Wednesday's horse-racing meet.

Hong Kong's stock exchange changed its rules this year to keep markets open during typhoons, with the operator telling Bloomberg News that it was "closely monitoring" the situation.

Authorities have told residents of low-lying areas to be alert to flooding, while opening 46 temporary shelters.

Ragasa -- named after the Filipino word for rapid motion -- will be closest to Hong Kong and nearby casino hub Macau on Wednesday morning, according to Chinese weather services.

- Shenzhen shelves bare -

Shelves of fresh meat and vegetables were mostly bare at a supermarket in Shenzhen's Bao'an District on Monday evening, AFP journalists saw.

Checkout queues were long in the bustling store as people hurried around to pick up supplies.

A supermarket employee told AFP that bread had already sold out by midday, adding, "It's not normally like this."

Guangzhou's rail authority said all train services will be suspended on Wednesday, according to the South China Morning Post.

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

The Philippines earlier evacuated more than 10,000 people and closed schools and government offices across the country in response to the super typhoon.

hol/aha

CATHAY PACIFIC AIRWAYS