Pakistan evacuated thousands of people from southern coastal areas ahead of a possible cyclone, two days after a storm killed at least 235 people in the port city of Karachi, officials said.

The meteorological department issued an alert saying that a tropical storm forming in the Arabian Sea 150 kilometres (90 miles) south of Karachi was likely to intensify into a cyclone in the next six to 12 hours.

The new storm was expected to bring strong winds with "heavy to very heavy rainfall" in Sindh province, of which Karachi is the capital, and neighbouring Baluchistan province, it said on its website.

Fishermen were advised to stay ashore until Thursday in some areas because of the likelihood of "extremely" rough seas. At least 10 fishermen have been missing since the weekend, officials said.

"It is likely to pass very close to Karachi and it can cause heavy rain. Even small rains cause destruction so naturally it can cause losses," meteorological department director Qamaruz Zaman told AFP.

Officials in Baluchistan said around 2,000 people had been evacuated to higher ground from areas along the Arabian Sea coast that were already inundated by the rain.

Karachi is still reeling from a deadly thunderstorm on Saturday, with parts of the sprawling port city of 12 million people still without electricity or drinking water.

The shortages have led to several riots.

Provincial health minister Syed Sardar Ahmed said that 228 people had been killed by the weekend's bad weather and another 200 injured, mostly in the suburbs of the city. Seven others were killed in Baluchistan, officials said.

Workers were clearing fallen trees and the wreckage of nearly 50 huge iron advertising billboards that collapsed during the thunderstorms, causing several of the casualties.

Most of the deaths were caused when the roofs and walls of shanty homes collapsed.

Relief camps have been set up in the badly affected Karachi slum area of Gadap Town where more than 1,000 shanty homes were destroyed, while two truck-loads of aid have been dispatched, city officials said.

President Pervez Musharraf ordered local authorities to take "immediate steps to tackle the situation," state media reported. Karachi Mayor Mustafa Kamal said a major relief operation was underway.

Some Karachi residents said they were forced to sleep in the open despite promises from municipal authorities to shift them to schools and private buildings.

"We are living in the open because we have lost our house and no one has provided us any shelter," said labourer Ghulam Rasool, 35.

The deputy mayor of Gadap Town, Abdus Sattar Brohi, said people were still waiting for the authorities to help. "People are paying from their own pockets to provide food to their neighbours in distress," Brohi told AFP.

Local media criticised Karachi authorities for allowing oversized billboards with weak foundations in congested areas. Prime Minister Shaukat Aziz told officials to deal with the billboard problem on a "war-footing."

The storm has also destroyed hundreds of houses in parts of Sindh and Baluchistan, officials said.

Monsoon rains meanwhile have claimed around 144 lives over the last four days in neighbouring western and southern India. The area has suffered heavy downpours and flash floods.