China has evacuated hundreds of thousands of people and ordered at least 10 cities to close schools and some businesses as the strongest storm of the year bears down on its southern coast.

Hong Kong city has upgraded its typhoon warning to No. 8 - just two levels below the maximum - ahead of the arrival of Super Typhoon Ragasa.

The storm is expected to make landfall in China's Guangdong province on Wednesday, where some 370,000 people have been evacuated so far, as authorities warn of a "catastrophic" situation.

Ragasa has been dubbed the "King of Storms" by China's meteorological agency and is expected to move towards northern Vietnam in the coming days, potentially impacting millions.

On Tuesday, supermarket shelves in Hong Kong were wiped empty of fresh bread, vegetables, meat and instant noodles as residents prepared to hunker down.

Hong Kong International Airport said it expected "significant disruption to flight operations" from 18:00 local time on Tuesday until the next day.

More than 500 Cathay Pacific flights are expected to be cancelled, while Hong Kong Airlines said it would stop all departures from the city.

In cities across southern China, shop owners piled sandbags in front of their stores in preparation for the storm's arrival, with residents in low-lying areas next to the sea front particularly worried about tidal surges.

Many have also taped up the windows of their homes and businesses, hoping to prevent their destruction.

While the island of Taiwan remained largely unscathed after Ragasa passed through overnight, at least six people were injured and more than 100 international flights cancelled.

Ragasa also lashed through a remote island in the north of the Philippines on Monday, killing at least one person as thousands of families were evacuated before the storm made landfall.

Schools and government offices were shut in large parts of the country, including in the capital Manila.

Super typhoon Ragasa - equivalent to a Category 5 hurricane - packed wind gusts of up to 285km/h (177mph) at its highest point on Monday, and has triggered warnings of floods, storm surges and landslides across the region this week.

Ragasa would "pose a serious threat" to Hong Kong, said Eric Chan, the city's Chief Secretary for Administration, comparing it to two other typhoons which left behind trails of severe destruction.

Super typhoon Mangkhut in 2018 - to date the most intense typhoon to strike the city - injured 200 people, sunk ships and wrecked infrastructure, with the weather agency estimating economic losses of HK$4.6bn ($592m).

In 2017, typhoon Hato unleashed serious flooding and injured more than 100 people in the city.