MANILA, Philippines - Aid workers helped by Filipino and U.S. troops took advantage of improving weather in the Philippines on Wednesday to distribute food and clear debris in areas slowly recovering from devastating floods, as a powerful new storm threatened Japan.

Typhoon Melor was gathering strength as it travelled along Japan's southern coast with sustained winds of about 160 kilometres per hour, causing power outages and disrupting air and train travel.

Japan's Meteorological Agency said the typhoon was expected to hit central Japan, including the Tokyo area, on Thursday. It said Melor could dump up to 50 centimetres of rain by Thursday evening, and issued warnings for strong winds, heavy rains and high waves along a broad swath of southern and central Japan.

In the Philippines, U.S. troops on counterterrorism exercises in the country's south were diverted to help deliver food, medicine and shelter to flood victims. Last week, hundreds of U.S. Marines and sailors based in Okinawa, Japan, brought in additional equipment, including five transport helicopters aboard two Navy ships.

Marine Capt. Jorge Escatell from Houston said Wednesday that U.S. forces were helping clear garbage and other debris from the flooded streets of Marikina in the capital region and distributed eight tons of food to Talim Island in the middle of Laguna Lake, south of Manila.

Metropolitan Manila Development Authority chief Bayani Fernando said more than 20,000 tons of garbage and other debris were clogging streets and waterways. He said it would take at least two months to clear the mountains of garbage.

In Japan, local governments in some parts of Tokyo made sandbags available to residents to protect their homes against flooding from rivers and canals. Rescue workers set up evacuation centres, and hundreds of public schools in the capital region were closed Thursday as a precaution.

The typhoon grounded more than 200 domestic flights connecting southern and western regions, with some 250 flights -- both domestic and international -- expected to be cancelled Thursday. More than 100 express trains were suspended.

Wild weather has battered many parts of Asia over the past two weeks, starting when Tropical Storm Ketsana dumped more than a month's worth of rain on the Philippine capital in just 12 hours. Some 300,000 Filipinos are still in emergency evacuation centres. Ketsana left nearly 300 people dead in the Philippines, 162 in Vietnam, 18 in Cambodia and 16 in Laos.

Eight days later, Typhoon Parma triggered landslides and floods that killed another 16 people in the Philippines but did not directly hit Manila.

The United Nations appealed Tuesday for $74 million -- the largest flash appeal ever launched for the Philippines -- for food, water, sanitation facilities and health care. The appeal has already received commitments of between $9 million and $10 million, UN humanitarian chief John Holmes said in New York.

Philippine Defence Secretary Gilbert Teodoro said the $74 million will be used to provide the most urgent needs of about a million storm victims. Rebuilding devastated homes and communities will be done later and would require more funds, he said.

UN representative Jacqueline Badcock said the government responded well to the calamity but was clearly overwhelmed. "The government has really tried its best," she said. "When you get something that really is unprecedented and catastrophic like the Manila flood, the government is not able to cope."