No fewer than 21 children were killed at an elementary school that collapsed in the Mexican capital when a powerful earthquake rattled the area on Tuesday, a government official said.

"We have a report of 25 dead, among them 21 children and four adults" at the Enrique Rebsamen elementary school, Mexican Undersecretary of Education Javier Trevino told the Televisa network.

At least 100 children are still missing after school building collapse.