Packing winds of 215km/h and gusts up to 295km/h, Ragasa slightly intensified as it brushed Babuyan Island and headed for possible landfall over Calayan Island, raising the risk of storm surges exceeding three metres, the state weather agency said.
The Babuyan islands remained under a high-level storm warning signal, with residents advised to stay away from coastal areas and riverbanks.
Video clips shared by disaster agencies showed the northern Cagayan province being pummelled by fierce winds and heavy rain, triggering strong waves and sending trees swaying violently.
The government suspended work and classes across Metro Manila and large parts of Luzon as outer rainbands began lashing the region, prompting warnings of power outages, landslides, floods, and dangerous seas.
Airlines have cancelled two dozen domestic flights, mostly serving Luzon's main hubs, while ports have suspended ferry services.
Although Ragasa will not directly hit Taiwan, its outer bands are expected to bring heavy rain to the island's sparsely populated east coast.Â
Taiwan has issued land and sea warnings, has cancelled 146 domestic flights, and has evacuated more than 900 people from mountainous southern and eastern areas.
Vietnam's defence ministry ordered its forces to monitor the storm and prepare for a possible landfall later this week.
Chinese authorities have activated flood control measures in several southern provinces, warning of heavy rain beginning Tuesday night.
Hong Kong has announced a 36-hour airport shutdown starting Tuesday evening, while Macau and Zhuhai are bracing for impact, with school closures and evacuation plans under way.
Hong Kong's airport would be closed from 10pm AEST on September 23 to 6pm AEST on September 25, Qantas said in a statement, adding it would contact customers who were affected.
In Hong Kong, long queues formed at supermarkets where products like milk had already sold out, while vegetables were being sold for more than triple their usual price at fresh markets, according to Reuters witnesses.
