Typhoon Goni, the most powerful storm this year, has made landfall in the Philippines with maximum sustained winds of 225km/h (140mph).
The state weather service said the typhoon hit Catanduanes island on Sunday at 04:50 local time (19:50 GMT Saturday).
It is expected to hit the main island of Luzon later in the day, passing over the capital Manila.
Almost a million people have been evacuated from their homes.
In a severe weather bulletin, the Philippine Atmospheric, Geophysical and Astronomical Services Adminstration (Pagasa) warned of “flooding (including flash floods), rain-induced landslides, and sediment-laden streamflows” in areas of Luzon, as well as the islands of Visayas and Mindanao.
“Within the next 12 hours, catastrophic violent winds and intense to torrential rainfall… will be experienced,” it said.
Goni – known as Rolly in the Philippines – is the most powerful storm to hit the Philippines since Typhoon Haiyan killed more than 6,000 people in 2013.
This time, preparations have been made complicated by the Covid-19 virus, which has already caused 380,739 infections and led to 7,221 deaths in the Philippines.
“We are having a hard time with Covid-19, and then here comes another disaster,” Senator Christopher Go, the top aide of President Rodrigo Duterte, told a virtual news conference.
Civil defence chief Ricardo Jalad said “almost a million” people in the eastern Bicol region of Luzon had left their homes.
Some 1,000 coronavirus patients in Manila and nearby Bulacan province currently housed in large isolation tents might be moved into hotels and hospitals, he also said.
Residents were being urged to prepare themselves for the possibility of widespread flooding and landslides as a result of the heavy rain and strong winds.
“Storm surges are imminent on our east coast,” Mark Timbal, of the National Disaster Risk Reduction and Management Council, told local broadcaster ABS-CBN. “We are monitoring Mayon and Taal volcanoes for possible volcanic mud flows.”
Ports and airports were shut, and schools, gyms and government-run evacuation centres were being used for emergency shelters.
“Evacuating people is more difficult at this time because of Covid-19,” Bicol regional civil defence spokesman Alexis Naz told AFP.
Relief goods, heavy machinery and personal protective equipment were being moved into areas of need, but a local mayor in Quezon province said the pandemic had depleted their funds for disaster emergencies.
The Philippines is hit by an average of 20 storms and typhoons a year. Some 22 people were killed last week when Typhoon Molave barrelled through the same region now braced for Goni.