Nick Clegg has said flood-hit Pakistan will need aid for years to come after he saw the extent of the devastation for himself.
Speaking after being shown aid camps near the southern town of Sukkur, one of the worst-affected regions, the Deputy Prime Minister said: "I think the sheer scale of this, it is really quite difficult to comprehend.
"The terrible thing is that it has got a long tail. It has got a lot of aftershocks that are going to last for a long time."
He said the response from countries around the world has been too slow, although he praised donations from the British Government and public.
"We have to make a huge effort to provide important emergency aid but really stick with this for the long term," he said.
Mr Clegg said flood waters have not drained away in many areas, creating a "real danger of diseases taking hold".
He also discussed the situation with Pakistan's president, Asif Ali Zardari, who was also touring the disaster scene, as well as briefing him on his visit to Afghanistan and talks with President Hamid Karzai the day before.
More details of how some of the British Government's £33 million of aid will be allocated were released to coincide with Mr Clegg's visit.
About £9 million will be spent on 2,330 water pumps for safe drinking supplies; emergency shelter kits for around 30,500 families; repairing or installing 5,000 toilets; spades, picks and wheelbarrows to help 1,600 families clear debris from their homes; and 650 kits containing essentials for newborn babies.
The money will be given to charities Save The Children, Concern and Oxfam.
