Manila  - Tropical storm Halong gained strength on Saturday as it moved toward the northern Philippines, prompting the weather bureau to raise storm alerts in several provinces.

The weather bureau said Halong, with maximum sustained winds of 105 kilometres per hour and gusts of up to 135 kilometres per hour, was expected to make landfall in the province of Ilocos Sur late Saturday.

"Residents along coastal areas of western Luzon and Western Visayas are alerted against big waves generated by this tropical cyclone," its bulletin said.

"Residents in low-lying areas and near mountain slopes are advised to take all the necessary precautions against possible flash floods and landslides," it added.

Halong was the second storm to hit the country in a week, heralding the start of the rainy season. (dpa)