Officials struggled at first to launch a rescue effort at the site, surrounded by marshland and hard to access with heavy equipment, and scores of victims remained buried under the rubble on Wednesday.

Planning experts and seismologists fear this disaster could be repeated on a massive scale, saying a major earthquake could destroy thousands of rickety buildings in the capital, Dhaka, and other cities.

"An earthquake measuring six or seven on the Richter scale will destroy 30 percent of buildings in Dhaka," said Shahid Alam, chairman of Dhaka Development Authority.

"Eighty percent of buildings will crumble if an eight magnitude quake hits," he told Reuters on Wednesday, adding that more than 300 tall buildings in Dhaka were described as high risk.

The capital, with its 10 million population, has large slum areas, and many homes, offices and factories are poorly constructed and at risk from major quakes.

The country's eastern border with Myanmar lies along an active fault where two large tectonic plates, the Indian plate and the Eurasian plate, are colliding.

"Bangladesh's Sylhet and Chittagong regions are high-risk areas where a major earthquake can strike," seismologist Mominul Islam told Reuters from Chittagong observatory in the south.

When a quake of about magnitude 5 hit in 1997, it killed 21 people in Chittagong.

Adding to the sense of unease, the impoverished country's authorities have yet to upgrade the country's sole geophysical observatory in Chittagong, which routinely fails to locate a quake's exact epicentre or measure its strength.

But Monday's factory collapse seems to have sent a chilling signal to senior government officials.

The country held its first ever quake drill in Dhaka on Tuesday, using firefighters, helicopters and everything needed to save people after a major tremor.

QUAKE DRILL

The Disaster Management Ministry said the drill was pre-planned and had nothing to do with the factory collapse. But people watching it, including President Iajuddin Ahmed and ministers, clearly looked concerned.

"We should go for more such exercises so we are prepared to face any real-life disaster," said Dhaka mayor Sadek Hossain.

The scene at the flattened Shahriar Fabrics factory at Palashbari, 30 km (18 miles) from Dhaka, shows the enormity of the challenge facing officials should a big quake strike.

It took many hours for heavy equipment to reach the factory site because the access road was narrow and authorities needed time to find cranes and excavators.

A major quake would be likely to leave rescuers struggling to clear blocked streets in time to reach survivors.

City officials say hundreds of high and medium-rise buildings have been built in fast-growing urban areas in recent years in violation of planning laws or without approval.

Such buildings stand every chance of coming down in the event of a big jolt. Also at high risk are innumerable old buildings that have not been repaired for generations, especially in Dhaka.

Alam of the Dhaka Development Authority said it was trying to get modern equipment such as excavators, cranes and heavy-duty bulldozers, and would use city parks to shelter patients if hospitals broke down.

Officials say Bangladesh was lucky to have been spared by last December's tsunami that killed more than 200,000 people along Indian Ocean shores. Only two people died in Bangladesh.

"But threats of tsunami in the coastal belt of the country cannot be ruled out," said Mahfuzur Rahman, director-general at the relief and rehabilitation ministry, at a post-tsunami international coordination meeting in France.

"It is essential that a rapid seismic observation system including hydro-accoustic sensors, sea-height buoys and modern tide gauges be developed in the country as it is an integral part of an tsunami early warning system."

Mir Fazlul Karim, director of the Geological Survey of Bangladesh, said earlier this month that Bangladesh would set up a National Tsunami Warning Centre, amid fears that earthquakes off the coast could trigger destructive waves.