Mangkhut's sustained winds weakened to 170 kilometres per hour with gusts of up to 260kph after it sliced across Luzon's flood-prone rice plains and mountain provinces toward the South China Sea, aiming at southern China and Hong Kong, where residents were bracing for the worst.
More than 4 million people could be affected by the typhoon as it lashes the country with high winds and drenching rainfall.
At least five people, including two responders tasked to help in disaster preparations, died as typhoon "Ompong" unleashed a fury of heavy rains and strong winds in Luzon and some parts of the Visayas, national officials said.
Poor communities reliant on fishing are some of the most vulnerable to typhoon winds and the storm surge that pounds the coast.
Mangkhut, which went ashore at about 1:40 am Hong Kong time in the Philippines' Cagayan province, could affect as many as 30.5 million people in its path across Asia, according to the United Nation's Global Disaster Alert and Coordination System.
The Joint Typhoon Warning Center U.S. Navy-U.S. Air Force command, located in Hawaii, had downgraded Mangkhut from a "super typhoon", when it had peak wind speeds of 180 miles per hour, prior to landfall on the country's largest and most populous island.
In southern China, ferry services in Qiongzhou Strait have been halted on Saturday morning as Mangkhut is approaching the provinces of Hainan and Guangdong, local authorities said.
"It felt like the end of the world. that was stronger than Lawin", said Saquing, 64, referring to a powerful super typhoon which hit the region in 2016.
In the Philippines, the storm has stoked fears that it may wreak as much damage as Typhoon Haiyan, which in 2013 devastated a vast swath of the country, killing more than 6,000 people.
Tolentino, who has been assigned by President Rodrigo Duterte to help coordinate disaster response, said at least two other people were missing and added that the death toll could climb to at least 16 once other casualty reports were verified.
Some 105,000 people in the Philippines were staying in temporary shelters after the mass evacuation of coastal areas following major storm surge warnings.
Thousands of evacuees have taken refuge in emergency shelters.
"We really learned a lot from the Haiyan experience", Catherine Cabarles, a school teacher in Quezon City, told NPR before Mangkhut arrived.
Earlier Friday, the storm passed over the US territory of Guam, knocking down trees and taking out 80 percent of the island's power.
People buy water and food at a supermarket ahead of the arrival of the Super Typhoon Mangkhut in Zhanjiang in Guangdong province, September 15, 2018. Cathay Pacific Airways Ltd. said in a statement it will ground 400 flights in the next three days.
The airline said the cancellations were due to typhoon Mangkhut, which has been battering the region with torrential rains and ferocious winds.
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.
Manghkut is forecast to move on to China's southern coast later this weekend.