The provincial governor of Pangasinan province, Amado Espino, told reporters that water released by the San Roque dam had flooded towns.
"The dam is supposed to be for flood control but now it is so filled it is like it is not there. The water just rushes right through from the mountains to Pangasinan."
Mr Espino said strong currents and continuing rain were making it hard to reach and rescue people in flooded areas.
The province's Vice Governor, Marlyn Premicias, told the Associated Press she had been receiving text messages from people needing to be rescued.
"Eastern Pangasinan has become one big river," she said.
Lt Col Ernesto Torres of the NDCC told Reuters news agency that 30,000 people had been evacuated in the province and 60-80% of the land was flooded.
The UN earlier appealed for $74m (£47m) to help victims of storms in the Philippines.
It says about 500,000 people have fled their homes and are still living in emergency shelters and has warned of an urgent need for food, water, sanitation facilities, emergency shelter and health care provisions.
Thousands of people have been stranded by floodwaters
Gwendolyn Pang of the Philippine National Red Cross told the BBC that getting aid to those in need was difficult as travelling by land was often impossible.
"Most of the areas are impassable because of landslides and because of the flood water, so we need to airlift relief food and also do rescues by airlift," she said.
Typhoon Ketsana hit Manila and surrounding areas on 26 September, causing the worst flooding in the capital in more than four decades.
Eight days later, Parma blew across the country's mountainous north, bringing more rain. Meteorologists say the storm is still lingering off the coast of the Philippines.
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