Forecasters said Typhoon Mangkhut could hit northern Cagayan province on Saturday. Cathay Pacific encouraged passengers travelling this weekend to and from Hong Kong to re-book and the airline would waive the fees.
"Although there are still uncertainties in the subsequent track of Mangkhut and its distance from Hong Kong, Mangkhut's extensive circulation will bring significantly deteriorating weather to Hong Kong on Sunday with frequent heavy squally showers".
Cagayan Gov. Manuel Mamba said by telephone that northern coastal and island villages in the typhoon's projected path will begin evacuating residents on Thursday ahead of the expected onslaught.
Super Typhoon Mangkhut, known as Super Typhoon Ompong in the Philippines, is now equivalent to a category 5 Atlantic hurricane, with winds of at least 252 kilometers per hour (157 mph), stronger than Florence, which is expected to cause massive flooding and devastation in the Carolinas.
Forecast of tropical storm Mangkhut.
Duterte issued the order during the command conference with weather, disaster, and other government officials at the National Disaster Risk Reduction and Management Council (NDRRMC) operations center in Camp Aguinaldo, Quezon City.
Office of Civil Defence chief Ricardo Jalad said more than 4 million people in the northeastern provinces of Cagayan and Isabela and outlying provincial regions are vulnerable to the most destructive effects near the typhoon's 125-kilometre (77-mile) -wide eye. Government agencies were conducting damage assessments and beginning to clear roads, according to the Pacific Daily News.
Schools and offices are being closed and farmers are racing to save crops. About 80 per cent of the United States territory was without power but it was restored by Thursday morning. The threat to agriculture comes as the Philippines tries to cope with rice shortages.
About 20 cyclones pass through the disaster-prone country each year. In 2013, Super Typhoon Haiyan which packed winds of as high as 315 kilometers per hour killed more than 6,300 people there.
Teams from the International Committee of the Red Cross are on high alert in northern Luzon, the Philippines where the storm is predicted to reach on Saturday morning.