Officials in Haiti say dozens of people, the majority of them children, died in the collapse of a school on Friday in the capital, Port-au-Prince.
Rescuers worked through Friday night under floodlights to find survivors in the remains of the three-storey La Promesse College in the suburb of Petionville.
Haitian Prime Minister Michelle Pierre-Louis told the BBC she believed about 700 people had been inside the concrete building when the roof caved in.
About 400-500 people have so far been rescued. More than 100 were injured, many seriously.
Ms Pierre-Louis said that when she visited the site, she had heard trapped children banging and crying for help.
Some survivors are believed to be still buried under the rubble.
People have been digging with their hands in a desperate attempt to free people while heavy machinery has been rushed to the scene.
Engineers from the UN mission in Haiti, Minustah, and members of the Haitian Red Cross are also at the scene, helping the local teams.
UN peacekeepers and local police have meanwhile been deployed to hold back the crowds of onlookers and the desperate relatives of those missing.
The authorities have blamed poor construction methods for the collapse of the building.