Storm warnings have been raised in 25 provinces across the main northern island of Luzon, restricting sea and air travel.
Heavy rains and gusts were already hitting the far northeastern tip of Luzon on Friday evening from the storm that forecasters said is the most powerful of 2018. They said the fast-moving typhoon has gained speed as it moves northwestward at 19 miles per hour.
The typhoon's peak winds were stronger than those of Hurricane Florence in the United States after it piled into the Carolinas, before it was downgraded to a tropical storm.
Government forecaster Rene Paciente warned that the storm "can lift cars".
In Cagayan's capital city of Tuguegarao, residents braced for the typhoon's fury by reinforcing homes and buildings and stocking up on food.
"We're anxious for the 10 million people in the Philippines living in the path of this destructive storm, including those who have been displaced several times due to the monsoon rains last July and August", Richard Gordon, chairman of the Philippines Red Cross, said in a statement.
The super typhoon's track could cause US$120 billion (S$165 billion) worth of damage, Bloomberg reported.
Officials have warned of storm surges of up to 6m and "very heavy damage" to vulnerable structures. Residents in the low-lying area of Tai O on Lantau Island would be taken to temporary shelters on Saturday.
As the powerful storm left the Southeast Asian archipelago and barrelled towards densely populated Hong Kong and southern China, search teams in the Philippines began surveying the provinces that suffered a direct hit.
"If we didn't, all of us would be dead", Abedes said.
"It's extremely risky as it's a very large system with very strong winds and a potential storm surge over a large distance", he said.
ASSOCIATED PRESS A convenience store is taped in preparation for approaching Typhoon Mangkhut in Hong Kong on Saturday
More residents are expected to move to safety as the Department of the Interior and Local Government (DILG) called on governors, mayors and village heads in four regions in the north to immediately evacuate all residents living in landslide and flood prone areas. According to Agriculture Secretary Emmanuel Piñol, the damage may reduce the country's rice supply and result in losses of up to 7.9 billion Philippine pesos ($146.2 million).
All flights will be cancelled between 2.30am on Sunday and 4am on Monday, while a small number of flights will have their scheduled departure times delayed until Monday.
The Hong Kong Observatory said the typhoon posed "considerable threat" to its residents, Al Jazeera reported. Thousands of shelters have been set up not only in the Philippines but also in China, where the storm is expected to hit later in the weekend.
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.
"It's still a life and death situation", he said.
"It would depend on the severity of the crisis", Duterte said.
"Yes, there are offers of global assistance from Australia and Japan right now, but we're still waiting for the assessment if there will be a widescale need for worldwide assistance", said Edward Yulo of the Department of Foreign Affairs (DFA).
Mangkhut 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.
The deadliest storm on record in the Philippines is Super Typhoon Haiyan, which also sparked category four alerts.
Hurricane Florence latest: Powerful storm to hit Carolinas on USA coast
Between downed trees and rising water levels, some major roads were impassable and more secondary roads were also cut off. A wind gust at the Wilmington airport was clocked at 105 miles per hour , the highest since Hurricane Helene in 1958.