At least 49 people were killed when a powerful, 7.1-magnitude earthquake rocked Mexico on Tuesday, toppling buildings in the capital and sowing panic on the anniversary of a devastating 1985 temblor. The preliminary toll from the authorities looked certain to rise, however, as it covered only regions close to Mexico City but not the capital itself, where 20 million people live. In Mexico City, emergency crews and hundreds of volunteers were digging through the rubble of collapsed buildings looking for survivors and bodies. "I'm so worried. I can't stop crying. It's the same nightmare as in 1985," Georgina Sanchez, 52, sobbed to AFP in a plaza in the capital."We ran outside thinking all was going to collapse around us," said Lazaro Frutis, a 45-year-old who escaped an office building before it crumpled to the ground. "The worst thing is, we don't know about our families or anything." The quake -- which occurred in the early afternoon, hours after city authorities had conducted an earthquake drill -- caused most of its damage in the center and south of the sprawling city.  Several buildings were reduced to debris and cars were flattened by falling masonry. Scenes of chaos permeated the city, with traffic jammed to a standstill and anxious people running between the vehicles, as ambulances tried to make headway, sirens squealing. Emergency officials warned people in the streets to avoid smoking because of the risk of igniting gas leaking from ruptured pipes. In several locations, people were seen clambering on buildings that were now piles of stone and tangled metal to seek survivors and bodies.   - 'Everyone was frantic' -   The disaster immediately recalled the 1985 quake in which more than 10,000 people died, escalating panic among the population. Jorge Lopez, a 49-year-old Spaniard living in Mexico City, said that when the quake happened he raced to the school in the central Roma district where his children aged six and three were, to find it collapsed but his offspring safe if terrified. "We arrived at the school and everyone was crying, everyone was frantic, and the kids were holding on to a rope," he said. "It's uncontrollable. You can't do anything against nature," he said. Witnesses said another school was smashed to rubble in Cuernavaca, a town just south of the capital. The fate of the pupils and teachers was unknown. An office building of around five stories in the chic Condesa district of central Mexico City collapsed. Volunteers scrambled among the debris, pulling out three survivors and looking for more. "There are people trapped there!" yelled one woman. Patients were evacuated from a hospital in the adjoining Roma district, wheeled out on beds and wheelchairs as staff set up makeshift wards outside. Mexico's president, Enrique Pena Neto, said on Twitter he had ordered the evacuation of damaged hospitals "and the transfer of their patients to other medical facilities." He said he was to hold an emergency coordination meeting after overflying the disaster zone. At one collapsed building in Roma, dozens of people clawed at the rubble as they waited for the arrival of heavy machinery to move the heavy chunks of stone. Officials called out for more volunteers, and for water. A woman standing and watching the efforts with her husband, a doctor, turned to him and said, "Darling, if you want to help, give me your glasses and take care." Unconfirmed social media posts suggested the city's international airport had closed because of damage. Mexico's stock market was shut because of the quake.   - Trump's prayers -   Officials in other countries began to react to the disaster, with many offering to help. "With rising casualties & many collapsed buildings, my thoughts are with those impacted by the Mexico earthquake. The UN is ready to support," tweeted the UN's emergency relief coordinator, Mark Lowcock. Costa Rican President Luis Guillermo Solis, who was in New York with other world leaders for a UN General Assembly, expressed his "solidarity" with the Mexican people. US President Donald Trump, who has forged an antagonistic relationship with Mexico since coming to office, tweeted: "God bless the people of Mexico City. We are with you and will be there for you." Justin Trudeau, the prime minister of Canada, tweeted: "Devastating news from Mexico City. My thoughts are with those affected by today’s earthquake - Canada will be ready to help our friends." Mexican Foreign Minister Luis Videgaray responded by saying "Mexico sincerely thanks the displays of international solidarity that we are receiving."