At least 15,000 people are believed to have been killed in the devastation wreaked by a massive cyclone.
An international aid effort is under way, with hundreds of thousands thought to be without clean water or shelter.
Some remote areas have yet to be reached by rescuers - meaning the figures could increase even further.
Speaking at a summit of business leaders in central London today, the Prime Minister said: "I believe nearly a million people are now in need of food aid and we will have to help the families of those where people have died.
"I want to pledge on behalf of the British Government that we will work with the whole international community to make sure that food aid is available to the people of Burma."
Cyclone Nargis smashed into Burma on Saturday, bringing winds of up to 120mph. More deaths were caused by a resulting 12-foot wave than the cyclone itself, according to the Burmese authorities.
In the city of Bogalay in the Irrawaddy river delta, 95% of homes are thought to have been destroyed.
UN Secretary-General Ban Ki-Moon said the organisation would do "whatever (possible) to provide urgent humanitarian assistance".
Despite initial concerns from the international community, the state's secretive ruling junta has agreed to accept aid - although there are still questions over how much access foreign teams will be allowed.
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Connor Fitzgerald (06/05/2008 at 15:39)
I think he should invite a few million Burmese to come to the UK and pay for them to live next door to Anthony in Accrington.
If he does that, at least he will 'court' a few more votes, and good lord, doesn’t he need them!
Ha...........