Evans Lescouflair, the Youth and Sports minister, told a briefing on Saturday that the death toll had risen to 84, with at least 150 more hurt.
As the death toll continued to rise, Rene Preval, the Haitian president, warned that there was no telling how many more bodies might be found.
"This morning we found a classroom with 21 inside, students and their professor, and they are all dead," said Preval, who along with Michele Pierre-Louis, the prime minister, went to oversee the rescue effort.
"It is still possible to find people who have been buried under the rubble alive, we have to stay hopeful"
UN Humanitarian and Resident Co-ordinator
"Right now we cannot say how many bodies we will have because the work is not yet finished."
Preval told the Associated Press news agency that he believed poor construction methods, including a failure to use reinforced steel, had been to blame for the tragedy.
"It's not just schools, it's where people live, it's churches," he said.
Builders had been adding a new floor on top of the La Promesse school when it collapsed, officials said.
UN engineers and soldiers from the UN mission in Haiti (MINUSTAH) worked to remove heavy pieces of concrete and to contain the large crowds of people gathered to help in the rescue efforts.
Joel Boutroue, the UN Humanitarian and Resident Co-ordinator in Haiti, told Al Jazeera: "We are entering a phase whereby the chaos is being replaced by a very orderly system … but the process is slow.
"The building itself is very shaky and may collapse if we are not careful, the search and rescue from France are risking their own lives by trying to go deeper into the building.
"It is still possible to find people who have been buried under the rubble alive, we have to stay hopeful, just a couple of hours ago they extracted two children alive from the school. There might be up to 200 children in the building.
"It was supposed to be a two-storey building, but they were building a third floor when it collapsed. A law enforcement mechanism is needed to reinforce the government of Haiti," he said.
US Agency for International Development (USaid) search and rescue teams were using digital cameras on long poles to search through the debris.
Local authorities had used their bare hands to pull bleeding students from the rubble before heavy equipment and international teams arrived late on Friday.
Crowds of screaming and crying parents searched for their children in the ruins, and roads around the school were so jammed with people that some rescuers had to be brought in by helicopter.
|Rescuers worked through the night in an attempt to find survivors [AFP]
Two of Chimene Rene's children were found alive, but two sons, Stevenson Casamajor, 13, and Jeff Casamajor, 15, were still missing.
"We've been everywhere. We've been to the hospital, we've been everywhere looking for them," she said. "It seems there is no more hope now because it seems that nobody will come out alive from the rubble."
Other officials said an investigation into the construction of the school and a survey of other education establishments that might be at possible risk is under way.
"This construction did not meet normal standards. We are going to ask the minister of education to make an inspection of all the schools built in the same way," Yvon Bissereth, a senator, said.