Typhoon Co-May, upgraded from a tropical storm overnight, follows days of monsoon rains that have killed at least 12 people and left another eight missing across the archipelago since July 18, according to the national disaster agency.

With maximum sustained winds of 120 kilometres (75 miles) per hour, the typhoon was expected to make landfall on the west coast in either La Union or Ilocos Sur province by Friday morning, the country's weather service said.

Around 70 domestic and international flights have been cancelled due to the storms, the civil aviation authority said.

The government has announced the suspension of classes across Luzon for Thursday.

Tens of thousands were evacuated across Manila earlier this week by floodwaters that swamped some neighbourhoods in waist-deep water and left residents of nearby provinces stranded and in need of rescue by boat.

As of Thursday, at least several thousand people in Manila remained unable to return to their homes.

"We cannot send them home yet because it is still raining and some typhoons are still expected to affect the country," Ria Mei Pangilinan, a rescue coordinator in the capital, told AFP.

"There might be more (evacuees) if the rain does not stop."

Typhoon Co-May was about 210 kilometres off the country's west coast as of 11 am (0300 GMT).

Tropical Storm Francisco, meanwhile, was situated about 735 kilometres from the country's east coast and on a trajectory towards northern Taiwan.

The two storms are not believed to be on a collision path.