Weather specialist Aldczar Aurelio of the Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa) said Tropical Depression "Neneng" brought light to moderate rains over the Batanes and Calayan group of islands on Monday as it formed 22 kilometers north of capital town of Basco.
According to the U.N. Global Disaster Alert and Coordination System, the super typhoon could affect as many as 43.4 million people before it fades away.
With the predicted path of the typhoon, it could also hit Taiwan and Hong Kong next.
Super Typhoon Mangkhut, an even more powerful storm than US -bound Hurricane Florence, was heading Wednesday for the Philippines, Taiwan and Hong Kong. The storm is expected to strengthen further in the next 24 to 48 hours, according to CNN Meteorologist Michael Guy, before it weakens slightly to a category 4 equivalent storm as it approaches the the Philippines island of Luzon.
The civil defence office in Manila said towns and cities on Mangkhut's path are preparing government buildings as evacuation centres, stockpiling food and other emergency rations, and preparing rescue teams and equipment.
The typhoon is arriving at the start of the rice and corn harvest season in Cagayan, a major agricultural producer, and farmers were scrambling to save what they could of their crops, Mamba said.
The Philippine Red Cross estimates three million Filipinos live in the direct path of Mangkhut, communications officer Mary Joy Evalarosa told AFP. The Pearl River Delta region, which includes Hong Kong and Macau, is among the most densely populated in the world.
In 2016, a super typhoon lashed southern parts of Cagayan, destroying tens of thousands of houses.
An advisory from the JTWC on Tuesday said Mangkhut was packing winds of up to 250 kilometers per hour (kph) near the center and gustiness of up to 306 kph.
Weather forecaster Aldczar Aurelio said Mangkhut will enter the PAR on Wednesday afternoon and storm signals may be raised by Wednesday evening.
Weathermen are keeping a close eye on two severe disturbances, including a "stronger" typhoon in the Pacific Ocean that is forecast to hit northern Luzon within the week.
With a massive rain band 900 kilometers (560 miles) wide, combined with seasonal monsoon rains, the storm could bring heavy to intense rains that could set off landslides and flash floods, state forecaster Meno Mendoza said.