The United Nations on Monday began a drive to feed half a million people affected by torrential rains in Pakistan where a second year of flooding has killed more than 200, officials said.

The crisis came just weeks after aid agency Oxfam accused the government of failing to invest in prevention measures after floods last year hit 21 million people and cost the economy $10 billion in the country's worst natural disaster.

Pakistan, a nuclear-armed state suffering appalling levels of Taliban and Al-Qaeda-linked violence, has now seen vast swathes of farmland inundated for a second year in the southern province of Sindh, the nation's breadbasket.

One official said the situation there was even worse than last year.

"So far, 209 people have been killed and 5.3 million affected," Zafar Qadir, head of the country's disaster management authority, told reporters.

"Around 1.7 million acres of agricultural land has also been affected by the rains and floods."

The UN food agency said Monday it had started to provide emergency supplies to the first of half a million people, following a weekend appeal from Pakistan, which already relies on billions of dollars of international aid.

World Food Programme (WFP) spokesman Amjad Jamal told AFP that the agency had provided food packages to more than 600 families in Badin, one of the worst affected districts of Sindh.

"This is the first UN food response after Pakistan's government's appeal. We will expand this program to half a million people in coming days," he said.

China, Pakistan's most trusted foreign ally, said it had pledged $4.7 million for urgent humanitarian assistance and its ambassador on Monday handed over a cheque worth $50,000 to the disaster management authority.

The authority said it was working to quantify "huge" losses with cash crops such as sugar cane, banana and cotton now under water.

The government was last year pilloried by flood victims who accused civilian authorities of a delayed and inadequate response to the disaster.

A special parliamentary committee, formed by Prime Minister Yousuf Raza Gilani to coordinate relief efforts this time round, said it was facing huge problems.

"We have provided 80,000 family food packages and 45,000 tents. We have procured 10,000 more tents but there are serious distribution problems," Qamar Zaman Kaira, a member of the committee, told reporters.

"The helicopters are unable to fly in the continuous rains and roads have been flooded. The crisis is worse than last year in Sindh province. There are huge losses."

Gilani has said recent rains in Sindh were nearly two-and-a-half times normal levels, and inundated 4.1 million acres, including 1.7 million acres of crops.

He said 700,000 houses had been damaged, 150,000 people in relief camps needed immediate assistance and that 64,000 livestock had been lost.

The UN children's agency said up to 2.5 million children in southern Pakistan had been affected by the floods.