Soldiers, police and civilian volunteers worked through the night after Tuesday's 7.1-magnitude quake, hoping to find survivors beneath the mangled remains of collapsed buildings in Mexico City and across a swath of central states.
"The armed forces and federal police will continue working non-stop until every possibility of finding more people alive is exhausted," Interior Minister Miguel Osorio Chong said on Twitter.
The most agonising search was at a school in the capital where 21 children and five adults were crushed to death, and where at least 30 children were still missing.
"No one can possibly imagine the pain I'm in right now," one mother Adriana Fargo, who was standing outside what remained of the school waiting for news of her seven-year-old daughter, said.
The nation's attention was fixed on the school, the Enrique Rebsamen elementary and middle school on Mexico City's south side.
Hundreds of soldiers, police and volunteers wrestled with the wreckage through the night trying to extract a teacher and two students found alive beneath the rubble.
President Enrique Pena Nieto, who rushed to the site, warned that the death toll could rise.
Suspicion was already mounting of shoddy building standards at the school.
The three-storey building "ought to have had in-built earthquake resilience," said geoscience professor David Rothery of the Open University in Britain.
"Had it been properly constructed it should not have collapsed, and I expect questions will be asked about whether the appropriate building codes were adhered to."
Nowhere to go
Parks and plazas in the center of Mexico City were meanwhile flooded with people unable or afraid to return home for the night after the quake caused their walls to sway and crack.
At Parque Mexico, in the swank neighborhood of Condesa, nervous evacuees set up an impromptu kitchen to serve meals for rescue workers.
The destruction revived haunting memories in Mexico on the anniversary of another massive quake in 1985 that killed more than 10,000 people, the disaster-prone country's deadliest ever.
Tuesday's quake struck just two hours after Mexico held a national earthquake drill, as it does every September 19 to remember the 1985 event.
People gather around to help the search effort as the death toll continues to rise.
Adding to the national sense of vulnerability, the earthquake struck just 12 days after another quake that killed nearly 100 people in southern Mexico.
Experts said the two quakes did not appear to be related, as their epicenters were far apart.
Mexico sits atop five tectonic plates, making it particularly vulnerable to earthquakes.
The death toll as of early Wednesday was 217, the head of the national disaster response agency, Luis Felipe Puente, wrote on Twitter.
There were 86 dead in Mexico City, 71 in Morelos, 43 in Puebla, 12 in Mexico state, four in Guerrero and one in Oaxaca, he said.
Rescue workers reported that families were getting WhatsApp messages pleading for help from desperate relatives trapped under debris.
Patients were evacuated from the capital's hospitals, wheeled out on beds and wheelchairs.
Mexico City's international airport closed for more than three hours following the quake. The stock market was forced to shut, but was set to reopen Wednesday.
In Puebla, a picturesque colonial city near the quake's epicenter, several churches were damaged and one collapsed, killing 11 people, officials said.
Prayers from the Pope and Trump
Pope Francis said he was praying for Mexico.
"In this moment of pain, I want to express my closeness and prayer for all the beloved people of Mexico," he said during his audience on Saint Peter's Square in the Vatican.
Even US President Donald Trump, who has forged an antagonistic relationship with Mexico, tweeted his sympathies.
"God bless the people of Mexico City. We are with you and will be there for you," Trump wrote.
And German Chancellor Angela Merkel's spokesman tweeted her condolences.
"Solidarity with Mexico. Our deepest sympathies to those who have lost loved ones. All the best to the rescue teams," the message said.
