At least 30 people, mostly children, died at a primary school which collapsed in Mexico City during Tuesday’s earthquake, local media say.
The shallow, 7.1 magnitude quake killed at least 225 people in total and caused major damage across states in the centre of the country.
Desperate searches for survivors under the rubble are continuing.
Dozens of buildings were toppled, much of the electricity supply was cut and broken gas mains sparked fires.
The tremor struck shortly after many people had taken part in an earthquake drill, exactly 32 years after another quake killed thousands in the capital.
Mexico is prone to earthquakes and earlier this month an 8.1 magnitude tremor in the south left at least 90 people dead.
Though it struck a similar region, Tuesday’s earthquake does not appear to be connected with the quake on 7 September, which was at least 30 times more energetic, the BBC’s Jonathan Amos writes.
As many as 37 people – 32 children and five adults – died when Enrique Rébsamen primary school collapsed in Mexico City’s southern Coapa district, Efe news agency reports, quoting local media.
According to Mexican news site Reforma, 30 bodies have been found at the school and 22 people are missing.
More than 500 members of the army and navy, along with 200 police officers and volunteers, have been working at the site, Mexican newspaper Milenio says.
“Some voices have been heard,” Mexican President Enrique Peña Nieto said after visiting the rescue operation.
“In the time I have been here, I have seen how at times they have asked for total silence, solidarity to listen for the voices.”
At least 209 schools were affected by the quake, 15 of which have suffered severe damage.