Rescuers are racing against the clock to reach survivors trapped under the rubble of a school in Mexico City which collapsed during Tuesday’s earthquake.

One is a 12-year-old girl who is believed to be sheltering under a table, but rescuers say they do not know how to reach her.

At least 21 children and five adults died as the school collapsed.

It was one of dozens of buildings toppled by the quake. At least 230 people are known to have died.

President Enrique Peña Nieto has declared three days of mourning for the victims.

As rescue operations continued for a second day, attention was focused on the Enrique Rébsamen primary school, in Mexico City’s southern Coapa district, where the body of a female teacher was found overnight.