Philippine rescuers raced Thursday to reach residents still stranded by flooding in the hard-hit Bicol region, after torrential rains from Tropical Storm Trami (Kristine) submerged villages and killed more than 20 people.

Schools and government offices were shuttered across the northern Philippines as the storm made landfall on the country's main island of Luzon after first paving a trail of destruction south of the capital.

"As of 7 am, we have 20 dead (throughout the Bicol region)," regional police chief Brigadier-General Andre Dizon told reporters Thursday, adding the figure had yet to be finalized. "Most of them from drowning or buried in landslides."

In Naga city and the town of Nabua, rescuers were using boats to reach residents still stranded on rooftops.

"They are seeking assistance through (Facebook) posts and that's how we learned about them," Bicol police spokeswoman Luisa Calubaquib told AFP.

According to the national weather service, the eye of the storm was passing over the northern Philippines' mountainous interior as of 8 am (0000 GMT) with maximum sustained wind speeds of 95 kilometers (59 miles) per hour.

It was predicted to exit the island within 12 hours.

More than 30,000 people were forced to evacuate in Bicol on Wednesday, police said, as "unexpectedly high" flooding turned streets into rivers.

Lorie Dela Cruz of the state weather bureau told AFP a month's worth of rainfall had been dumped in the region in a 24-hour window from 8 am on October 22 to the following morning, with Camarines Sur province and Albay province's Legazpi city particularly hard hit.

On Thursday, rescuers were searching for a missing fisherman after a boat sunk in the waters off Bulacan province, west of Manila, the local disaster agency told AFP.

"Rescuing people was difficult since the wind was strong and was causing a strong current," said Geraldine Martinez, a rescue officer in Bulacan's Obando municipality.

A day earlier, 11 people drowned in floodwaters in the Bicol city of Naga, according to local police chief Erwin Rebellion.

In Quezon province, southeast of the capital, an elderly woman drowned, while a toddler was also killed after falling into a flooded canal, police said.

Manila's civil defense office reported one person was killed by a falling tree branch.

Storms and typhoons are common around the region at this time of year.

However, a recent study showed that they are increasingly forming closer to coastlines, intensifying more rapidly and lasting longer over land due to climate change. 

About 20 big storms and typhoons hit the Philippines or its surrounding waters each year, damaging homes and infrastructure and killing dozens of people.