HONG Kong and southern China hunkered down under red alert Sunday as strong winds and heavy rain from Typhoon Mangkhut lashed the densely populated coast.

The terrifying storm swept through a day after it left at least 28 dead from landslides and drownings in the northern Philippines.

The South China Morning Post reported the typhoon would remain a signal number 10 storm through the afternoon - Hong Kong’s most severe weather warning.

The Post also reported Mangkhut is roaring towards two nuclear power stations in mainland China’s Guangdong province, where the typhoon is expected to make landfall later today, according to the Associated Press.

Taishan and Yangjiang nuclear power stations were reported to be “in combat readiness mode”, with operators understood to be taking no chances after Japan’s devastating Fukushima incident in 2011, where three nuclear reactors went into meltdown.

Nearly half a million people had been evacuated from seven cities in Guangdong province, where Mangkhut is expected to make landfall later today. The gambling enclave of Macau closed down casinos for the first time and the Hong Kong Observatory warned people to stay away from the Victoria Harbour landmark, where storm surges battered the waterfront reinforced with sandbags.

The national meteorological center said southern China “will face a severe test caused by wind and rain” and urged officials to prepare for possible disasters.

The world's strongest storm so far this sliced across the northern tip of Luzon Island on Saturday, a breadbasket that is also a region of flood-prone rice plains and mountain provinces with a history of deadly landslides.

More than 5 million people were in the path of the typhoon, equivalent to a Category 5 Atlantic hurricane when it hit the Philippines. This morning, it packed sustained winds of 155 kilometres per hour and gusts of up to 190km/h.

China and the Philippines agreed to postpone a visit by Chinese Foreign Minister Wang Yi that was to start today due to the typhoon’s onslaught, which caused nearly 150 flights, a third of them international, to be cancelled and halted sea travel.

The Hong Kong Observatory said although Mangkhut had weakened slightly, its extensive, intense rainbands were bringing heavy downfall and frequent squalls. Storm surge of about 3 meters or above is expected at the city’s waterfront Victoria Harbour, the observatory said, appealing on the public to avoid the shoreline.

Francis Tolentino, an adviser to Philippine President Rodrigo Duterte, said the 25 died mostly in landslides and houses that got pommeled by the storm’s fierce winds and rain. Among the fatalities were an infant and a 2-year-old child who died with their parents after the couple refused to immediately evacuate from their high-risk community in a mountain town in Nueva Vizcaya province, Tolentino said.

“They can’t decide for themselves where to go,” he said of the children, expressing frustration that the tragedy was not prevented.

Tolentino, who was assigned by Duterte to help co-ordinate disaster response, said at least two other people were missing. He said the death toll could climb to at least 16 once other casualty reports were verified.

Mayor Mauricio Domogan said at least three people died and six others were missing in his mountain city of Baguio after strong winds and rain destroyed several houses and set off landslides, which also blocked roads to the popular vacation destination. It was not immediately clear whether the deaths and missing cited by Domogan had been included in Tolentino’s count. Authorities were verifying the drownings of three people, including two children. About 70 men reportedly returned to their coastal village in Cagayan to check on their homes as the storm drew closer Friday, but Tolentino said he had received no reports of the men figuring in an accident.

About 87,000 people had evacuated from high-risk areas of the Philippines. Tolentino and other officials advised them not to return home until the lingering danger had passed.

In Cagayan’s capital, Tuguegarao, where the typhoon made landfall, Associated Press journalists saw a severely damaged public market, its roof ripped apart and wooden stalls and tarpaulin canopies in disarray. Outside a popular shopping mall, debris was scattered everywhere and government workers cleared roads of fallen trees. Many stores and houses were damaged but most residents remained indoors as occasional gusts sent small pieces of tin sheets and other debris flying dangerously.

The Tuguegarao airport terminal also was damaged, its roof and glass windows shattered by strong winds.

The typhoon struck at the start of the rice and corn harvesting season in Cagayan, a major agricultural producer, prompting farmers to scramble to save what they could of their crops, Cagayan Gov. Manuel Mamba said. In Hong Kong, Security Minister John Lee Ka-chiu urged residents to prepare for the worst.

Cathay Pacific said all of its flights would be cancelled between 2:30am local time on Sunday and 4am. Monday.

“Because Mangkhut will bring winds and rains of extraordinary speeds, scope and severity, our preparation and response efforts will be greater than in the past,” Lee said. “Each department must have a sense of crisis, make a comprehensive assessment and plan, and prepare for the worst.” In nearby Fujian province in China, 51,000 people were evacuated from fishing boats and around 11,000 vessels returned to port on Saturday morning. China’s National Meteorological Center issued an alert saying Mangkhut would make landfall somewhere on the coast in Guangdong province on Sunday afternoon or evening.

Ferry services in the Qiongzhou Strait in southern China were halted on Saturday and helicopters and tugboats were dispatched to Guangdong to transfer offshore workers to safety and warn ships about the typhoon, China’s official Xinhua News Agency reported.

Mangkhut, the Thai word for mangosteen fruit, is the 15th storm this year to batter the Philippines, which is hit by about 20 a year and is considered one of the world’s most disaster-prone countries. In 2013, Typhoon Haiyan left more than 7,300 people dead or missing, flattened villages, swept ships inland and displaced more than 5 million in the central Philippines.