UN emergency relief chief, Jan Egeland, said the organisation had never seen such a “logistical nightmare”.
Nato began flying in 900 tonnes of aid on Thursday, but Mr Egeland said a massive airlift was also needed to bring people out of remote areas.
Pakistan says nearly 50,000 people died in areas under its control.
Mr Egeland said only $86m had been pledged of the £312m the UN had asked for to fund the relief operation – and far less actually received in hard cash.
