The death toll from a powerful earthquake that rocked Mexico on Tuesday has surged to 248 people, the head of the national disaster response agency, Luis Felipe Puente, said on Twitter.
The dead included at least 21 children crushed beneath a primary school that collapsed on Mexico City's south side during the 7.1-magnitude quake, authorities said.
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 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.
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.
Parks and plazas in the centre 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 neighbourhood 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.
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 epicentres were far apart.
Mexico sits atop five tectonic plates, making it particularly vulnerable to earthquakes.