A house in Bato Town in Camarines Sur Province on Luzon of the Philippines is isolated by floods caused by Storm Trami. Photo by AFP
The national weather service said Usagi, the archipelago's fifth major storm in three weeks, was likely to make landfall Thursday in Cagayan province on the northeast tip of main island Luzon.
Provincial civil defence chief Rueli Rapsing said mayors had been ordered to evacuate residents in vulnerable areas, by force if necessary.
"Under (emergency protocols), all the mayors must implement the forced evacuation, especially for susceptible areas," he told AFP by telephone, adding as many as 40,000 in the province lived in hazard-prone areas.
The successive storms have taken a toll on the resources of both the government and local households, the UN said late Tuesday.
About 210,000 of those most affected by recent flooding need support for "critical lifesaving and protection efforts over the next three months", the United Nations Office for the Coordination of Humanitarian Affairs said in a statement.
"Typhoons are overlapping. As soon as communities attempt to recover from the shock, the next tropical storm is already hitting them again," UN Philippines Resident and Humanitarian Coordinator Gustavo Gonzalez said.
"In this context, the response capacity gets exhausted and budgets depleted."
A sixth storm, Tropical Storm Man-yi, currently near Guam, is expected to hit the Philippines as early as next weekend.
Gonzalez urged "resource partners to support the UN effort and fill "critical funding gaps".
The initiative "will help us mobilise the capacities and resources of the humanitarian community to better support government institutions at national, regional and local levels," he added.
Currently packing winds of 120 kilometres (75 miles) an hour, the storm is expected to bring severe winds, heavy rain and rough seas.
More than 28,000 people displaced by recent weather events are still living in evacuation centres operated by local governments, the country's civil defence office said in its latest tally.
Government crews were still working to restore downed power and communication lines and clearing debris from roads.
About 20 big storms and typhoons hit the archipelago nation or its surrounding waters each year, killing scores of people and keeping millions in enduring poverty.
A recent study showed that storms in the Asia-Pacific region are increasingly forming closer to coastlines, intensifying more rapidly and lasting longer over land due to climate change.