A huge and powerful typhoon is headed toward southern China after lashing the Philippines with destructive winds and torrential rain, putting the region’s megacities on high alert with cancelled flights and disruptions to schools and businesses.

Tens of millions of people could be impacted by the storm, which is expected to pass south of the major cities of Hong Kong, Macau, Shenzhen and Guangzhou, before making landfall again in mainland China’s Guangdong Province.

Typhoon Ragasa hit the northern Philippines as the strongest storm on earth so far this year, after generating sustained winds of over 267 kph (165 mph), the equivalent of a Category 5 hurricane.

The storm, known in the Philippines as Nando, made landfall as a super typhoon over Panuitan Island, in the northern Cagayan province, on Monday, according to the country’s meteorological agency (PAGASA).

Ragasa has since weakened slightly and is no longer a super typhoon, according to the Joint Typhoon Warning Center. However, the storm remains a powerful typhoon with sustained winds of 145 mph (230 kph), making it the equivalent of a Category 4 hurricane.

Authorities in China have activated emergency responses. Entire megacities in Guangdong, one of the world’s most populous regions, have been brought to a standstill ahead of the storm, with schools closed and work suspended, some businesses shut, and public transport halted.

Guangzhou, a city of 18.6 million people, may issue its highest red alert on Tuesday, while in Shenzhen, home to about 17.5 million residents, officials were preparing to relocate 400,000 people from low-lying and coastal areas.

Supermarket shelves were emptied in Hong Kong as residents stockpiled supplies in preparation, and video showed similar scenes in the southern Chinese cities of Zhuhai and Shenzhen.

Hundreds of flights have been disrupted across the region, with cancelations in Taiwan, Hong Kong and southern China. Hong Kong-based airline Cathay Pacific said it will stop passenger flights scheduled to leave and arrive in the city on Tuesday evening until Thursday morning. Hong Kong Airlines, another regional carrier, also suspended dozens of flights for the week.

A mega bridge linking Hong Kong, Macau and the Chinese city of Zhuhai will also be closed from Tuesday.

Landslides, flooding in Philippines

The extent of the damage in the Babuyan Islands is not yet clear. The Philippines had warned of “life-threatening” conditions on the islands as Ragasa’s dangerous winds triggered flooding and landslides.

A landslide in Benguet, on Luzon Island, killed one person and injured several others, according to the Tuba Public Information Office. Video posted by the Philippines Coast Guard in northern Luzon’s Ilocos Norte shows teams rescuing families from the heavy winds and torrential rain.

More than 10,000 people were evacuated across northern and central Luzon ahead of the storm, the Philippines Department of the Interior and Local Government said in a statement.

Video from Camiguin Island, posted by the department, showed fierce winds and ocean water whipping past houses onto a residential street. Further north, footage filmed by a resident showed ferocious gusts of wind pelting tall trees in the Batanes province.

Heavy rain advisories remain in place for much of the northern Philippines as Ragasa’s outer bands continue to lash the country, with further risks of flooding and landslides possible in Luzon.

Ragasa is expected to continue a slow weakening trend as it moves closer to Hong Kong and southern China Tuesday and Wednesday, likely as the equivalent of a Category 3 hurricane with winds near 115 mph (185 kph), according to the JTWC.

The storm will continue moving to the west-northwest, ultimately making landfall in western portions of Guangdong Province Wednesday evening local time.