Unicef has trebled its appeal for funds to help women and children in flood-stricken Pakistan.
The charity is calling for £90 million in donations, a dramatic increase from its request for £30 million issued previously.
The new figure reflects the fact that the scale of the disaster is placing unprecedented strain on supplies and the need remains vast, the organisation said.
Among the needs it identified were: access to sanitation and safe drinking water to lower the risk from water-borne diseases for six million women and children; five million aqua tabs for water cleaning, one million plastic buckets, one million jerry cans and one million soap bars; three million sachets of oral rehydration salts and 1.5 million doses of zinc for two million children under five suffering from diarrhoea in the south of the country; vaccinations against preventable diseases such as measles and polio, which can spread quickly in cramped dirty conditions, for 1.5 million children under the age of five.
The call for help came as actor Ewan McGregor filmed an appeal for Pakistan's children with the charity.
Launching the appeal, McGregor said: "We've all seen the shocking pictures on the news about the floods in Pakistan. These floods have affected more people than the Haiti earthquake and 2004 tsunami combined and, as in all disasters, it's the children who have been hardest hit - an estimated 3.5 million children in Pakistan are now in need of urgent help."
Jemima Khan, Robbie Williams, David Beckham, Sir Roger Moore and TV host Cat Deeley are also supporting the campaign, Unicef said.
Meanwhile, the head of another aid appeal for the country praised the "extraordinary" generosity of the British public after donations topped £40 million.
Disasters Emergency Committee (DEC) chief executive Brendan Gormley said the response was "unprecedented" after week-on-week donations soared by more than 70%.
:: Donations can be made to Unicef online at www.unicef.org.uk or by calling 0800 316 5353. The public can also donate by texting FLOOD or FLOODS to 70099 to make a £3 contribution to the appeal. The public can donate to the DEC by calling the 24-hour hotline on 0370 60 60 900, visiting www.dec.org.uk or donating over the counter at any post office or high street bank, or sending a cheque. They can also donate £5 by texting the word GIVE to 70707.