The Red Cross is calling for $A84 million to help some of the more than 10 million people left devastated after Typhoon Haiyan in the Philippines.
While the death toll is not yet known, authorities fear the body count will top 10,000.
Simon Eccleshall, of the International Federation of Red Cross and Red Crescent Societies, said the typhoon was one of the biggest to make landfall.
"What we are witnessing unfolding in the Philippines is a major humanitarian catastrophe," he told a media briefing in Sydney on Tuesday.
Mr Eccleshall said half a million people were displaced with 9.8 million directly affected.
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The Red Cross is appealing for 87 million Swiss francs ($A84 million) to urgently provide household supplies, such as sleeping bags, water, food and mosquito nets, to 100,000 struggling families.
However, that funding will be for initial assistance only, with the appeal expected to expand in coming weeks.
Mr Eccleshall said the organisation was "first and foremost interested in saving lives and in doing that we need to get people on the ground provide life saving" services.
Authorities warn it will be several days before the full scope of the situation is understood.
Mr Eccleshall said the recovery would be lengthy and the Red Cross was looking at years of assistance to help communities get back to normal.
The typhoon, which saw winds above 300 km/h, came on the back of 7.2 magnitude earthquake that struck Bohol and flooding in recent months.
