MEXICO CITY (AFP) - Allegations of negligent construction and oversight began to fly on Monday (Sept 25) after deadly building collapses during Mexico's earthquake, as hope faded of finding more survivors of a disaster that killed more than 300 people.

The most-watched collapse site - a school where 19 children were killed last week - was built illegally on land reserved for housing, according to local media reports.

Mexico City's mayor, the education minister and the top official for the district all traded blame after reports that the Enrique Rebsamen primary school operated using false documents.

"If confirmed, it would be very serious," Education Minister Aurelio Nuno told TV network Televisa, saying he had ordered an investigation.

The government has also come in for criticism from anguished families of people still missing after Tuesday's earthquake.

"All they tell us are lies," said Anel Jimenez, 42, whose cousin Martin Estrada, a 30-year-old accountant, was inside a seven-story office building when it collapsed.

"No one from the government has come to show their face. They just send low-profile officials who always have clean helmets and shiny shoes. They just come to see what they can get out of other people's pain."

Political analysts said the quake underlined politicians' lack of credibility, less than a year out from presidential elections.

Just 35 per cent of Mexicans approve of President Enrique Pena Nieto's response, according to a poll by the newspaper Reforma.

"Anger with the political class will be the political aftermath of the earthquake," said the Eurasia Group consulting firm.

"This shows the deeply rooted discontent which is likely to continue."

Rescue workers have now wrapped up their efforts at all but five sites in Mexico City, and the chances of pulling any more survivors from the rubble are dim.

But Pena Nieto has been careful to insist that authorities will not send in bulldozers to start cleanup until rescuers are absolutely certain there are no more people in the rubble.

The building where Estrada's cousin was located, at 286 Alvaro Obregon Avenue in the trendy Roma neighborhood, is now the main search site. It crumpled into a tangled heap of concrete and steel with 132 people inside.

Twenty-nine people were rescued alive from the building in the first days, and 69 across the city.

But since late Friday (Sept 22), only bodies have been recovered.

In Mexico City, people began to warily return to work and school.

After nearly a week of eerie quiet in the sprawling city of 20 million people, the capital's notorious traffic jams were starting to appear again.

Of the capital's 8,700 schools, 103 reopened on Monday, the education ministry said. The rest were due to resume classes in the coming days, after undergoing architectural inspections.

The stakes are high for an already widely criticised government. After an earlier earthquake on Sept 7, all schools were given a clean bill of health.

But the city was shocked by the primary school collapse that killed 19 children and seven adults.

An aftershock that shook Mexico City on Saturday (Sept 23) has made the country all the more jittery.

And the sense of vulnerability has only been heightened by the fact that Tuesday's (Sept 19) earthquake struck on the anniversary of a 1985 quake that killed more than 10,000 people, the worst in Mexican history.

Mexico is particularly earthquake-prone, sitting atop five tectonic plates.

Many people are still on edge and suffering from post-traumatic stress, said psychologist Raquel Gonzalez, part of a team offering free counseling sessions in a park at the heart of the disaster zone.

"The people who come feel like the ground is still moving. They're very afraid," she told AFP.

The latest death toll stands at 325 people - 186 of them in Mexico City.