Relief officials said around 250,000 people had been left homeless and at least 21 killed by Cyclone Yemyin, which hit the area on Tuesday just days after thunderstorms left around 230 people dead in the southern port city of Karachi.

"The rain is continuing and has badly affected our relief efforts. Planes and helicopters are standing on runways awaiting clear weather," Khuda Bakhsh Baloch, the relief commissioner of badly-hit Baluchistan province, told AFP.

A military statement said 10 army helicopters were on standby to carry out rescue operations as soon as the weather permitted. It was the second successive day that the rain and wind had kept them grounded.

A C-130 Hercules transport aircraft carrying relief goods was also on standby at Chaklala airbase near Islamabad to fly to Baluchistan, again subject to the weather clearing, it added.

Pakistani troops had evacuated some 4,500 people from some of the worst hit areas along the coast, the statement said.

Baloch said that Baluchistan's rail and road links had been damaged by flooding. Gas and electricity supplies to most parts of the province were also cut after a main pipeline and power cables were washed away.

Cyclone Yemyin is the second major storm of the north Indian Ocean cyclone season after Cyclone Gonu hit Oman, Iran and southwestern Pakistan in early June, killing more than 60 people.

The United Nations said on Wednesday that the destruction in Pakistan -- plus floods in neighbouring India and extreme weather across Europe -- showed the world must be better prepared to cope with the impact of climate change.