The huge, slow-moving typhoon made landfall near the town of Casiguran on the island of Luzon on Sunday morning.
Koppu brought winds of close to 200km/h (124mph) and whipped up coastal surges 4m (12ft) high.
Three days of torrential rain has been predicted, triggering major flooding and possibly landslides.
Alexander Pama, head of the government's main disaster agency, said 10,000 people had been displaced in north-eastern Luzon but no casualties had been reported so far.
Initially, we are getting [reports that] many houses were destroyed, power lines toppled and trees blocking major roads," he said.
The eye of the storm was moving west at a speed of just 3km/h (2mph).
"It has slowed almost to a crawl. We were hoping it would speed up and spare us sooner," Mr Pama added.
Flights and ferry services in the north have been cancelled and some bus services in mountain areas suspended due to the threat of landslides.
On Friday, President Benigno Aquino made a televised warning, the first time he had done so since Super Typhoon Haiyan in 2013, which killed more than 6,300 people.
BBC science editor David Shukman, who is in the capital Manila, says public warning systems have been greatly improved since Typhoon Haiyan, so there is a much better chance of keeping people safe.
source: Bbc
