Some four million people were expected to have set off from the capital Dhaka by late Tuesday to spend the holiday with their families, leaving the normally teeming streets of the city deserted.

But the traditional exodus by train, bus and ferry, many of them dangerously overloaded, was being hampered by the thick fog.

"Launches (ferries) that were supposed to set out at 6:00 am did not set out until 6:00 pm on Monday because of the fog and many launches could not get to the terminal at all," Joynul Abedin, deputy director of Dhaka's main ferry terminal, told AFP Tuesday.

Thirteen additional ferries with searchlights had been pressed into service to try to reduce the backlog with captains forced to order silence on board so they could listen for the sound of other boats to avoid collisions, he added.

Eid al-Adha, or the feast of sacrifice, is Islam's second biggest annual festival and marks the prophet Abraham's readiness to sacrifice his son Ismael on the orders of God.

The Muslim holy book, the Koran, says the archangel Gabriel offered a lamb in Ismael's place after Abraham passed the test of his faith by raising his dagger toward his son.

Millions of animals including cows, goats, camels and sheep are slaughtered each year to mark the festival, for which the government has declared a three-day national holiday.

Bangladesh, with a population of 140 million, has the world's third largest Muslim population.

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