Deadly super typhoon Mangkhut is on a collision course with southern China's vulnerable megacities after tearing through the Philippines and killing at least 16 people.
Meanwhile flight chaos has descended on Hong Kong as tens of thousands of flights have been delayed or cancelled due to the damaging storm.
At least 543 flights have already been scrapped affecting 96,000 passengers, according to the South China Morning Post.
The Air New Zealand website shows that a flight scheduled to leave Hong Kong for Auckland at 18.10 has already been cancelled and warns that more may follow.
Mangkhut made landfall Friday on the northeastern tip of Luzon island in the Philippines where it tore off roofs, felled trees, triggered 42 landslides and caused extensive flooding.
The superstorm set off landslides and destroyed homes in the Philippines, killing at least 16 people and displacing tens of thousands as it left the Southeast Asian archipelago and turned toward southern China.
Almost all buildings in the city of Tuguegarao — the capital city of the northeastern Cagayan province — sustained damage, according to a government official.
It's the most powerful storm on the planet this year with top-of-the-scale Category 5 winds of 185km/h.
The system is back out over open water — weakened, but headed across the South China Sea toward China where it is expected to cause more death and destruction in the country's densely populated southeast coast.
Bureau of Meteorology Australia tropical climatologist Greg Browning told news.com.au the super typhoon was tracking west to Hong Kong and southern China, jeopardising millions more lives.
Experts have forecast the typhoon to make landfall in mainland China, somewhere between Yangjiang and Wenchang in Hainan province, on Sunday afternoon or Monday, local time.
The Global Disaster Alert and co-ordination System (GDACS) said it expected a "high humanitarian impact based on the storm strength and the affected population in the past and forecasted path" of destruction. As many as 43 million people could be exposed to Mangkhut's cyclonic winds, according to the GDACS.
More than 500 flights have been cancelled at one of the world's busiest airports in Hong Kong in preparation for when the storm passes on Sunday.
Cathay Pacific said in a travel advisory on Saturday to expect "severe disruptions" at Hong Kong International Airport.At least five international airlines, including Cathay and Singapore airlines, have announced delays. They are expected to last for at least three days.
A Cathay Pacific flight scheduled to arrive in Auckland at 9pm this evening is also among those affected.
The China Meteorological Administration on Saturday maintained its yellow alert for the approaching typhoon — the second-highest level on a four-tier scale — after warning that the region could be put to "a severe test".
On the Chinese mainland, the three southern provinces of Guangdong, Guangxi and Hainan are co-ordinating preparations, including suspending transport and moving people to shelter inland, the national meteorological agency reported. The area is home to a string of megacities and more than 100 million people. Guangdong, China's manufacturing hub, has set up 3777 shelters, while more than 100,000 residents and tourists have been moved to safety or sent home. The province has recalled more than 36,000 fishing boats to port, while train services between the cities of Zhanjiang and Maoming have been suspended and all ferry services between the Guangdong and Hainan have been put on hold.
There are fears the superstorm could affect two nuclear power plants on its projected path. Emergency officials are on standby at The Taishan Nuclear Power Plant and Yangjiang Nuclear Power Station, both in the Guangdong province.
"All emergency personnel are at their posts and have conducted their preparatory work," officials said in a statement.
Hong Kong is also likely to be impacted. The Hong Kong observatory's tracking system shows a 70 per cent probability that Mangkhut could deviate within a 500km radius from its predicted position, causing uncertainty over the next few days. The observatory warned of rough seas and frequent heavy squalls, urging residents of the densely populated financial hub to "take suitable precautions and pay close attention to the latest information" on the storm.
Australian expat Alexis Galloway, who lives in Hong Kong, told news.com.au the government this morning "announced on the radio they are opening 47 emergency shelters".
"This is the first time I'm actually quite nervous (about a typhoon) … we live right on the water too and 15 minutes from Shenzhen! Right in the thick (of it)," she said.
The system is already stronger than any of the 15 past severe or super typhoons that warranted the highest "No 10" warning sign, the South China Morning Post reports.
Browning said Mangkhut was the most powerful storm system to have developed on Earth this year but that it wasn't the strongest since records began in 1946, as has been reported internationally. Typhoon Haiyan — which killed more than 7,000 people when it lashed the Philippines with maximum sustained winds of 230km/h and gusts of 325km/h in 2013 — holds that record.
According to Browning, Mangkhut was "significantly stronger" than Hurricane Florence, which is simultaneously ripping the US state of North Carolina.
"(Mangkhut is) relatively rare (because it's) at the top of the severe scale," Browning said.
"It's extremely dangerous as it's a very large system with very strong winds and a potential storm surge over a large distance.
"There will be very heavy rainfall associated with it which has potential to cause widespread damage."
Earlier, the Joint Typhoon Warning Center in Hawaii categorised the system as a "super typhoon" which Browning said equates to "very destructive winds" and heavy rainfall that's likely to cause infrastructure damage anywhere it hits.
"But the biggest killer of all with a system like this is typically the storm surge," he said.
"The region close to the typhoon's crossing can expect (to bare the brunt)."
With a 900km wide rain band — which is 50 per cent bigger than Haiyan's — combined with seasonal monsoon rains, the typhoon could also set off more landslides, according to forecasters.
Countries across east and southeast Asia have issued emergency alerts and ordered evacuations as both Mangkhut and a second storm, Typhoon Barijat taunt the region.