A strong tropical storm barreled toward the Philippines Sunday, threatening the disaster-prone nation's east coast with giant waves, flooding and landslides, civil defence officials warned.

Forecasters said Tropical Storm Melor could strengthen into a full-fledged typhoon by Monday afternoon when it is expected to strike the central island of Samar.

"We should not underestimate the dangers posed by this storm," civil defence chief Alexander Pama told a meeting of rescue officials.

No evacuations were ordered, but authorities said they could be if the storm, with gusting winds reaching 140 kilometres (87 miles) an hour, hits the impoverished farming island of Samar which is home to 1.5 million people. The storm was moving west-northwest over the Pacific Ocean Sunday.

Food packs and other emergency items were stockpiled in the areas forecast to be hammered by Melor and the military was put on standby to evacuate people if necessary.

Heavy rain, flooding and landslides were forecast in areas within 150 kilometres of its eye between Monday and Wednesday.

Melor is expected to cut across Samar, Masbate, Marinduque and Mindoro islands before heading out to the South China Sea near Manila early by Wednesday.

Storm surges, or giant crashing waves, were also a risk in some areas said Pama, executive director of the National Disaster Risk Reduction and Management Council.

A tropical storm becomes a typhoon when maximum sustained winds are stronger than 120 kilometres, according to the state weather service. Melor had maximum sustained winds of 110 kilometres an hour on Sunday morning.

The Philippines is battered by an average 20 typhoons or storms a year, many of them deadly.

Typhoon Haiyan, the strongest to ever hit land, destroyed the central city of Tacloban and nearby towns in 2013 and left more than 7,350 people dead or missing.

Typhoon Koppu, the last deadly storm to hit the country, killed 54 people and forced tens of thousands of others to flee their homes in the northern Philippines in October.