Manila floods
Rescuers evacuate residents along a flooded street in Marikina city, Metro Manila - Reuters

The flood-ravaged Philippines capital of Manila has been bit by further heavy rains forcing thousands of residents to flee the city for higher ground.

The rainstorms and flooding are worse than previously thought, as nearly 60 to 80 percent of the city has been submerged.

At least 25 people have died and 300,000 are homeless. Five hundred makeshift shelters have been erected across the capital. Most schools and offices remain closed.

Rescue teams in rubber boats are looking for residents marooned on rooftops.

"Now that the waters are high again, they get scared and they are calling us to be rescued," police inspector Abner Perdosa told Associated Press.

The Philippines government has called for more volunteers to deal with the emergency. The city requires more hands to deliver food, water and medicine to an estimated two million people in the city.

The disaster council estimated that 450,000 families had been badly hit by the floods - the most destructive since 2009 when Typhoon Ketsana swamped almost 80 percent of the city.

Relief organisations said the scale of the disaster was huge and they did not have enough manpower to deal with the crisis.

"I can hear the sound outside my house of a very strong downpour. [In] many areas where the water receded, the water has gone up again. It's concerning us so much because many people are left in their homes," the Philippines National Red Cross's Gwendolyn Pang told Radio Australia.