More than 60% of the Philippine capital, Manila, is under water after more than a week of monsoon rain.
At least 19 people have been killed and more than 80,000 are being looked after in emergency shelters.
The national disaster agency describes the city as a waterworld with roads in some areas like rivers. The BBC reports a state of calamity has been declared in at least four areas.
Rescuers are using rubber boats to reach stranded people, but some have refused to leave amid fears of looting.
More than half the amount of rain normally seen in August has fallen in the capital in 24 hours.
President Benigno Aquino said the government does not have "infinite capabilities" to deal with the disaster.
Manila and the northern Philippines have been hit by constant bad weather since Typhoon Saola struck just over a week ago, killing more than 50 people.
Officials have warned that more rain is expected.
The current rain and floods are said to be the worst to hit the country since September 2009 when
Typhoon Ketsana brought flooding that killed more than 400 people. Typhoon Nestat and Nalgae struck two years later, leaving more than 100 dead.