Torrential rains have submerged much of the Philippine capital and surrounding areas and forced nearly 270,000 people to flee their homes.
Steady rains for the past ten days, which have left over 50 people dead, are set to continue until tomorrow.
The Philippines weather bureau said the rains are being fuelled by tropical storm "Haikui" in the Philippine Sea northeast of Taiwan.
The storm is headed for China's Zhejiang province, where over 250,000 people have been evacuated ahead of expected landfall late tomorrow.
Schools, financial markets, and public and private offices were ordered shut, including outsourcing firms whose corporate clients are mainly from the US and Europe.
Disaster officials said over half of Manila was swamped by floods as high as three metres, worsened by a high tide and the release of water from dams in surrounding provinces.
President Benigno Aquino, in an emergency meeting briefly interrupted by a power failure at the main army base in Manila, ordered officials to exert maximum effort to aid residents in flooded areas.
Officials have deployed army troops, police and emergency workers with rubber boats and amphibious trucks.
The monsoon rains, which dumped about 300mm or three times the daily average of 80-100mm from late last night, were the heaviest in three years, the weather bureau said.
Typhoon Ketsana, which swamped 80% of the capital in 2009, aided a monsoon downpour of more than 450mm in a 24-hour period.
Most major roads in Manila were inundated by knee-to waist-deep floodwaters. Some flights were delayed or cancelled and power, water and communications in flooded areas were disrupted.
Some of the affected residents were marooned on the roofs of their houses.