Large areas of Philippines towns and countryside were hit by the storms
The UN has appealed for $74m (£47m) to help flood victims in the Philippines.
UN humanitarian chief John Holmes said people there needed money for food, water, sanitation facilities, emergency shelter and health care.
Typhoon Ketsana left at least 300 people dead, and hundreds of thousands stranded. Typhoon Parma just over a week later caused further damage.
The Philippines has also said it will soon start importing rice to make up for the shortages caused by the storms.
The government usually imports large quantities of rice - the Philippines is the world's largest rice importer - but it is likely to begin importing it earlier than usual this year because so many crops have been damaged.
It traditionally imports from Thailand and Vietnam, although Vietnam was also hit by Typhoon Ketsana.
The Philippines will start its 2010 rice imports after a government panel determines the amount needed, the state's National Food Authority said - a process that could happen as early as this week.
But NFA spokesman Rex Estoperez warned consumers not to indulge in panic buying as supplies were adequate for the moment.
Philippines President Gloria Arroyo said food imports needed to be organised as soon as possible.
Total damage from the storms in the Philippines to crops, mostly rice, has reached 7.63 billion pesos ($164 million), the agriculture department said.
When launching its appeal for help in the Philippines, the UN said about 500,000 people have fled their homes and are still living in emergency shelters.
The UN's Humanitarian Co-ordinator, John Holmes, said the challenge was not only to raise money for the Philippines.
"Until this recent series of disasters in the Asia Pacific region, including in Samoa, we haven't a huge major natural disasters," he said.
"So I hope the donors will have money in their back pocket for the end of the year for the Philippines and also perhaps for Indonesia, because we're also talking to the government there about what we can do to help them," said Mr Holmes.
Disaster agencies say they are overwhelmed by the scale of disaster
To jump-start the response, Mr Holmes said he had authorised an immediate allocation of $7m from the UN's Central Emergency Response Fund.
The appeal has already received between $9m and $10m, he said.
The US Agency for International Development is giving $1.8m.
President Barack Obama has sent "deep condolences for the loss of life and devastation caused by recent storms in the Philippines".
The World Food Programme said it was providing helicopters and dinghies.
"Many needy people live in areas that still remain inaccessible because of the widespread flooding," WFP's director in the Philippines Stephen Anderson said in a statement from the UN agency's Rome headquarters.
At least 16 hospitals, as well as rural and community health centres, were damaged, the World Health Organisation (WHO) said.
WHO spokesman Paul Garwood said the risk of disease was heightened by the damage to water and sanitation systems.
"There are fears of outbreaks of communicable diseases, as yet there have been no reported major outbreaks," he added.
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.
A third typhoon, Melor, blew into Philippine waters on Monday but shifted course and was heading toward southern Japan where it is expected to make landfall on Thursday.