Typhoon Kalmaegi was approaching the Philippine coast and was forecast to slam the shore later on Monday, as authorities warned that torrential rains could batter the region.

Typhoon Kalmaegi is forecast to rapidly strengthen as it heads toward Vietnam's central coast, with winds potentially reaching up to 166 kph when it enters the East Sea on Wednesday, according to the National Center for Hydro-Meteorological Forecasting.

Australians planning holidays or already travelling in Southeast Asia are being urged to stay alert as a powerful storm system barrels toward the region.

More than 150,000 people have been evacuated across the eastern provinces of the Philippines as Typhoon Kalmaegi, locally named Tino, approaches from the Pacific. Authorities have issued warnings for torrential rains, potentially destructive winds, and storm surges reaching up to three metres (nearly 10 feet).