MANILA, Sept 28, 2009 (AFP) - Authorities in Manila were Monday scrambling to prevent disease outbreaks as putrid water lay across vast sections of the Philippine capital following the worst floods in over 40 years, officials said.

Sanitation conditions at overcrowded evacuation centres, where tens of thousands of people have sought refuge, are also deplorable with human faeces lying in the open at some of them, AFP reporters on the scene observed.

"Our surveillance is continuing in evacuation centres for possible outbreaks and epidemics," Health Secretary Francisco Duque said on government television.

"Our health teams are bringing in water and (products for) sanitation and hygiene at evacuation centres to make sure that disease does not spread." Health authorities were particularly concerned about typhoid and leptospirosis, a bacterial infection, that could be spread by dirty water, Duque said.

Saturday's disaster saw tropical storm Ketsana drop the heaviest rain in more than 40 years on Manila and neighbouring areas of Luzon island.

The nine-hour deluge left some areas of Metro Manila, a sprawling city of 12 million people, under six metres (20 feet) of water as poor drainage systems and other sub-standard infrastructure exacerbated the problem.

Eighty percent of the city was submerged and some areas remained more than knee-deep in water on Monday.

The government said the official death toll was 86, with another 32 people missing and more than 435,000 others displaced. The number of people killed is expected to rise.