Forecasters said typhoon, considered as the strongest this year, could hit northern Cagayan province on Saturday..
The weather bureau classifies a cyclone as a supertyphoon if its top sustained winds exceed 220 kph.
On Guam, a U.S. territory, residents woke up on Tuesday to flooded streets, downed trees and widespread power outages after Mangkhut passed through overnight.
"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".
The eye of the typhoon was forecast to go through the northern tip of Luzon, the main Philippine island, on Friday, he added.More news: Trump made false claim about economy, GDP, unemployment rate: White House
"The pre-emptive evacuation is going on in our coastal municipalities, the villages that are prone to storm surge", local government spokesman Rogelio Sending told AFP.
"We are on the wrong side of this storm, where most of the damage is done", Cooper said later in the day.
Presidential Spokesperson Harry Roque said supplies and assets needed to provide assistance to areas that would be affected by the typhoon have already been prepared by the concerned agencies.
Schools were shuttered and some farmers took to their fields to start early harvest of corn and rice that could be ruined by flooding.
An average of 20 typhoons and storms lash the Philippines each year, killing hundreds of people and leaving millions in near-perpetual poverty. In 2013, Super Typhoon Haiyan killed more than 6,300 people in the Philippines.More news: Olivia Newton-John is battling cancer for a third time
"Hong Kong as of the forecast now will be on the right quadrant of the storm with the greatest impacts from wind, rain and storm surge along that coast line", he said.
"It will bring destruction". A super typhoon is one with winds of 241 kilometres per hour (150 miles per hour) or greater.
While there was still uncertainty in its path the observatory said it could still pose very rough swells, flooding or a backflow of seawater to low-lying areas on the coast of Guangdong.
As the system continues to get close to the PAR i.e. the Philippine area of responsibility, it is likely to intensify even further into a Cat 5 Typhoon.More news: Aaron Rodgers Leads Packers to Comeback Win After Dramatic Return from Injury
With a massive raincloud band 900 kilometers (560 miles) wide, combined with seasonal monsoon rains, the typhoon could bring heavy to intense rains that could set off landslides and flash floods, government forecasters said.