HONG KONG — The Philippines braced Thursday for the onslaught of Super Typhoon Mangkhut, whose 150-mile-an-hour winds were on a path for a direct hit at the country’s largest and most populous island.

The military and the police in northern Luzon were placed on red alert — barring all troops from going on leave — so they could respond to emergencies in communities expected to bear the brunt of the typhoon, which packed the wind power of a Category 5 hurricane.

The typhoon appeared likely to strike an area considered the breadbasket of the Philippines, raising fears of significant damage to the agricultural sector, which has already been reeling from a series of typhoons that destroyed crops, livestock and fisheries.

The storm could bring “ruinous rain to central Luzon, home to the country’s agricultural land,” warned Richard Gordon, a senator and the chairman of the Philippine Red Cross. The typhoon is coming at the start of the corn and rice harvest, and farmers were urged to bring in as much of their crops as they could to minimize the damage.