Authorities put the death toll from Tuesday’s 7.1-magnitude quake at 272 people, but it was expected to rise further with more than 200 still missing in Mexico City.
Volunteers fought off growing fatigue to remove tons of rubble at dozens of flattened buildings in the capital and across several central states.
Experts say the average survival time in such conditions is 72 hours, depending on injuries.
In the capital’s central neighborhood of Roma, rescue workers scrambled to locate 23 people believed to be in the wreckage of a collapsed seven-story office building.
They have already pulled 28 survivors from the mountain of rubble. No deaths have been reported at the site so far.
Relatives of the missing waited in anguish for news.
Aaron Flores’s sister Karen and friend Paulino Estrada were both trapped inside.
Estrada managed to contact his family by cell phone, even making a video call. But there has been no news from Karen Flores.
“We’re feeling disoriented and desperate because we haven’t heard anything from her,” said her brother, 30.
At other locations, hope turned to grief.
“At 1:00 p.m. they pulled my mother’s body out of the debris, but identified her under a different name, and it wasn’t until 5:00 p.m. that they gave us the bad news,” said Maria Dolores Martinez, 38, at a Mexico City morgue.
A psychologist offering free counseling outside the morgue, Aldo Munoz, said: “Unfortunately our country has many open wounds, and people who have directly suffered violence and have lost loved ones in the earthquake really need psychological help.”
Authorities put the overall death toll at 137 people in Mexico City, 73 in Morelos state, 43 in Puebla, 13 in Mexico state, five in Guerrero and one in Oaxaca.
However, the situation on the ground was still chaotic, and figures in areas were rising — and sometimes falling.
Highlighting the confusion, one story that gripped the world’s attention turned out to be false: that of a girl supposedly trapped alive beneath the rubble of a school that collapsed in Mexico City.
Authorities denied Thursday that the girl existed.
“We have carried out a full count with the directors of the school and we are sure that all the children are either safe at home, in the hospital or unfortunately died,” Angel Sarmiento, a top officer in the Mexican marines, told journalists at the ruins of the Enrique Rebsamen school on the capital’s south side.
“There are indications there may be an (adult) still alive in the rubble. There are traces of blood in the photographs, as if the person had dragged him or herself and may still be alive.”
Rescue workers had previously told journalists they were certain a girl was trapped beneath the rubble, but the different versions of the story varied.
The story made headlines around the world after the quake, injecting a ray of hope into a tragedy that killed 19 children and six adults at the school.
But real stories of hope continued to emerge from ruined buildings across the city, where more than 10,000 people lost their lives in a devastating earthquake in 1985.
In the north of the city, a man who had been trapped for 26 hours and a 90-year-old woman were pulled alive from the rubble.
President Enrique Pena Nieto said authorities were not giving up the search.
“The rescue and support effort in the buildings that collapsed is still on. We are not suspending it. We have to keep up the rescue effort to keep finding survivors in the rubble,” he said during a visit to the state of Puebla, where the epicenter was.
US President Donald Trump called Pena Nieto and offered assistance. A US search-and-rescue team had arrived in Mexico, the American embassy said.
Rescue teams have also flown in from Israel, El Salvador and Panama and more were expected from Costa Rica, Ecuador, Honduras, Colombia and Spain.
Tuesday’s tragedy struck just two hours after Mexico held a national earthquake drill, as it does every year on the 1985 anniversary.
A system of quake sensors was set up in 1993 along the Pacific coast, where tremors are more common.
People in Mexico City were not warned by the system on Tuesday because the epicenter was only 120 kilometers (75 miles) outside the capital and thus outside the main area of sensor coverage, said Carlos Valdes of the National Center for Disaster Prevention.