"We were terrified and prayed as we stayed under a table for hours after strong winds blew away the roof and walls of our house," said one survivor,
Andres Subang, 72, wiping away tears as he told of how his family made it through the disaster.
"I have experienced countless typhoons in my lifetime, but this was the worst. It left nothing, we have no food and no more livelihood."
British-based forecaster Tropical Storm Risk downgraded Koppu to a tropical depression, but Philippine weather authorities retained a storm alert in the northern islands of Batanes and Babuyan.
Farm officials said flooding destroyed 5 percent of expected fourth-quarter production in the rice-producing provinces nationwide.
Authorities in the coastal town of Casiguran, where Koppu made landfall as a category 4 typhoon, are deploying heavy equipment to clear roads of uprooted trees, toppled electric posts and debris.
"When we went around the town, we saw the typhoon's destructive impact, there were so many houses destroyed," municipal official Nida Coralde told Reuters, adding that distribution of relief supplies had begun.
Strong winds reduced people's homes to matchwood, leaving them with nothing, said one survivor, as residents began work to repair homes.
Strong winds grounded military planes and helicopters on Tuesday, forcing the government to send in food, water and other relief materials by road. Some areas were still flooded, without power and communication links.
The Philippines is hit by 20 typhoons every year, on average.