The death toll after the collapse of a school in Haiti has risen to 82 after rescue workers uncovered a room with 21 dead, many of them children.

Rescuers worked through the night under giant generator- powered lights in a shanty town on the outskirts of the Haitian capital, Port-au-Prince, to search for survivors in the rubble of the three-story La Promesse school, which caved in yesterday while class was in session.

President Rene Preval, who was at the scene early today, said searchers dropped water and biscuits through holes in the rubble to a group of children and focused their efforts on reaching them.

At least 124 people were injured.

Rescue workers from the French Caribbean island of Martinique arrived at the scene to help cut through the rubble. A US rescue team was expected shortly.

A new storey had been under construction atop the school when it fell in, also destroying or damaging five homes next to it.

In Paris, French Foreign Minister Bernard Kouchner expressed his 'deep emotion' over the tragedy and promised to send 'as soon as possible a civil security team to help the Haitian authorities in rescuing the victims who are still buried.'

As many as 700 students aged from three to 20 attend the church-run school in a suburb of the capital, but an accurate count of how many had been inside when it crumbled is not yet available.