Mangkhut entered the Philippines as a super typhoon in the early hours and ripped over the main island of Luzon with winds of more than 200 kph (125 mph) and torrential rains.
More than 5 million people were at risk from the storm, which the Hawaii-based Joint Typhoon Warning Center downgraded from a super typhoon but one that is still punching powerful winds and gusts equivalent to a category 4 Atlantic hurricane.
Thousands of people fled their homes in high-risk areas ahead of the storm's arrival because of major flooding and landslide risks.
With a massive rain cloud band 560 miles wide, combined with seasonal monsoon rains, the typhoon could bring heavy to intense rains that could set off landslides and flash floods.
Cheng said the Hong Kong Observatory might issue a typhoon signal No 8 at "a relatively early time" on Sunday which may be followed by a signal No 9 or 10, depending on the storm's proximity to the city and its wind strength.
A man inspects debris blown onto the road at Tuguegarao in Cagayan province on Saturday, as Super Typhoon Mangkhut began to batter the Philippines. It was moving northwest at 15.5 miles per hour and was expected to leave the Philippines later that night.
Nearly all buildings in the city of Tuguegarao - the capital city of the north-eastern Cagayan province - sustained some damage, a government official said, and communications were down in places.
'It can lift cars, you can't stand, you can't even crawl against that wind, ' Paciente said.
Mangkhut could be one of the strongest storms to have an impact on Hong Kong in more than six decades.
Formerly classified as a super typhoon, Mangkhut is known as Ompong in the Philippines - as NPR's global correspondent Julie McCarthy reports, the government gives it a "Filipino cast" to engage the public.
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"Last time we had a super typhoon, there were 14,000-plus of totally destroyed houses and about 40,000-plus of partially destroyed houses", he told news channel ANC.
Wong said officials hoped to send elderly people living alone in Tai O to shelters on Saturday afternoon while buses would also be arranged to help residents in parts of Tuen Mun and Yuen Long to move away.
Expect "severe disruptions" at Hong Kong International Airport as Typhoon Mangkhut approaches the city this weekend, said Cathay Pacific in a travel advisory on Saturday (Sep 15).
"If we didn't, all of us would be dead", Abedes said.
Here an elderly resident of the town of Aparri on the north coast of Luzon is seen during the high winds and rain.
Fears have been raised about the storm's possible effect on agriculture in Cagayan and Isabela, where the bulk of the Philippines' rice is grown.
Chinese authorities in Guangdong province have called back more than 30,000 fishing boats and taken precautions at two nuclear power plants that are in the storm's path.
"Typhoon is coming", he said.
"It's still a life and death situation", he said.
In the meantime, Duterte tasked Ilocanos in his Cabinet to go home to their provinces to monitor government response to Ompong, Roque said.
"My appeal is that we need to heed the advice of the authorities".