Mexicans have packed churches to pray for the victims of the country's deadliest quake in 32 years as rescue teams search against the odds for any survivors trapped under rubble.
As another aftershock jolted southwestern Mexico on Sunday, the death toll from Tuesday's 7.1 magnitude earthquake climbed to 320 people.
With thousands of buildings damaged, survivors slept on the street outside their homes and estimates of the cost of the earthquake ran as high as $US8 billion ($A10 billion).
Many have been traumatised by the second major quake to strike Mexico City in their lifetime after a devastating 1985 tremor killed an estimated 10,000 people.
In the Basilica of Our Lady of Guadalupe, the national shrine of the majority Roman Catholic country, thousands of people gathered to pray.
"I came to ask God for strength for those who lost loved ones and for the Virgin to watch over us and keep us safe," said 69-year-old Maria Gema Ortiz. "Thanks to all those who came from other countries to help. Thanks to all and long live Mexico!"
Makeshift places of worship have popped up next to the crumbling cement and mangled steel of collapsed buildings in the deeply religious country.
In upscale Roma, one of the hardest-hit neighbourhoods of the capital, a priest led mass for nearly two dozen people under a blue tarp while a nun handed out small cards with an image of the Virgin of Guadalupe, who according to the Catholic faith first appeared to an Aztec convert in 1531.
More than 44,000 public schools in six states were due to reopen on Monday, but only 103 of the 4,000 public schools in Mexico City would open so as not to impede rescue and relief efforts.
Rescuers have narrowed their search to a handful of buildings in the sprawling metropolitan area of 20 million people, using advanced audio equipment to detect signs of life beneath tonnes of rubble, with help from teams from as far afield as Israel and Japan.
