AUTHORITIES in the Philippines have begun evacuating thousands of people in the path of the most powerful typhoon this year.

Schools are being closed, bulldozers are being prepared to deal with landslides, and rescuers and troops are on full alert in the country's north.

The Joint Typhoon Warning Centre in Hawaii categorised the storm as a super typhoon with powerful winds and gusts.

Forecasters said Typhoon Mangkhut could hit north-eastern Cagayan province on Saturday. It was tracked on Thursday about 450 miles away in the Pacific with sustained winds of 127 miles per hour and gusts of up to 158 mph).

With a massive rain cloud band 900 560 miles wide, combined with seasonal monsoon rains, the typhoon could set off landslides and flash floods, government forecasters said. Storm warnings have been raised in 25 provinces on the main northern island of Luzon, restricting sea travel.

Office of Civil Defence chief Ricardo Jalad said more than 4 million people in the north-eastern provinces of Cagayan and Isabela and outlying provincial regions are vulnerable to the most destructive effects near the typhoon's 77-mile-wide eye.

Nearly 48,000 houses in those high-risk areas are made of light materials and vulnerable to Mangkhut's ferocious winds.

Cagayan Governor Manuel Mamba said that evacuations of residents from coastal villages and island municipalities north of the rice and corn-producing province of 1.2 million people have started, and classes at all levels have been cancelled.

"The weather here is still good but we're moving them now because it's very important that when it comes, people will be away from peril," Mamba said.

The typhoon was slightly changing its track, he said, adding that authorities needed to rapidly reassess where to redeploy emergency teams and supplies.

The typhoon is approaching at the start of the rice and corn harvesting season in Cagayan, a major agricultural producer, and farmers were scrambling to save what they could of their crops, Mamba said. The threat to agriculture comes as the Philippines tries to cope with rice shortages.

The Office of Civil Defence said other northern provinces also started evacuating residents on Thursday from high-risk areas, including in northern mountain provinces prone to rain and mudslides.

Residents covered glass windows with wood, strengthened houses with rope and wooden braces and moved fishing boats to safety.

President Rodrigo Duterte cancelled his appearance at a missile test firing aboard a navy ship off northern Bataan province due to the approaching typhoon and instead led a meeting with disaster response agencies and defence officials in Manila.