A magnitude 7.1 earthquake rocked central Mexico, killing at least 138 people as buildings collapsed in plumes of dust and thousands fled into the streets in panic.
The quake came less than two weeks after another quake left 90 dead in the country's south, and it occurred as Mexicans commemorated the anniversary of a 1985 quake that killed thousands.
Dozens of buildings collapsed into mounds of rubble or were severely damaged in densely populated parts of Mexico City and nearby states. A column of smoke rose from a structure in one central neighbourhood in the capital.
Mexico City's mayor said 30 are dead in the capital alone.
The state of Morelos, just south of Mexico City, saw the highest death toll, with officials reporting 54 deaths.
An injured man is pulled out of a building that collapsed during an earthquake in the Roma Norte neighborhood of Mexico City. (Photo / AP)
The state of Puebla, where the epicentre of the quake struck, saw at least 26 deaths, the governor said.
At least four people were killed in the capital, while nine people were left dead in the neighbouring state of Mexico, officials said.
There were no immediate official reports of deaths in the capital, but journalists witnessed some people who had apparently died.
Rescue workers rushed to the site of damaged or collapsed buildings in the capital, and reporters saw onlookers cheer as a woman was pulled from the rubble.
Rescuers immediately called for silence so that they could listen for others who might be trapped.
Mariana Morales, a 26-year-old nutritionist, 26, was one many who spontaneously participated in rescue efforts.
Volunteers search a building that collapsed after an earthquake, in the Roma neighborhood of Mexico City. (Photo / AP)
A man enters a damaged building after an earthquake in Mexico City. (Photo / AP)
She wore a paper face mask and her hands were still dusty from having joined a rescue brigade to clear rubble from a building that fell in a cloud of dust before her eyes, about 15 minutes after the quake.
Morales said she was in a taxi when the quake struck, and she out and sat on a sidewalk to try to recover from the scare. Then, just a few yards away, the three-story building collapsed.
Gala Dluzhynska said she was taking a class with 11 other women on the second floor of a building on the trendy Alvaro Obregon street when the quake struck and window and ceiling panels fell as the building began to tear apart.
LIVE: Mexico City Airport closed & evacuated after 7.1M earthquake to SE of city. Flights diverting. Runway inspection ongoing. pic.twitter.com/mFsfAyjZuz— Airport Webcams (@AirportWebcams) September 19, 2017
She said she fell in the stairs and people began to walk over her, before someone finally pulled her up.
"There were no stairs anymore. There were rocks," she said.
They reached the bottom only to find it barred. A security final came and unlocked it.
The quake caused buildings to sway sickeningly in Mexico City and sent panicked office workers streaming into the streets, but the full extent of the damage was not yet clear.
Alarms blared and traffic stopped around the Angel of Independence monument on the iconic Reforma Avenue.
Electricity and cellphone service was interrupted in many areas and traffic was snarled as signal lights went dark.
The US Geological Survey calculated its magnitude at 7.1 and said it was centred near the Puebla state town of Raboso, about 125km southeast of Mexico City.
Puebla Governor Tony Galil tweeted that buildings were damaged in the city of Cholula including collapsed church steeples.
Earlier in the day workplaces across the city held readiness drills on the anniversary of the 1985 quake, a magnitude 8.1 shake, which killed thousands of people and devastated large parts of Mexico City.
A woman speaks on her cell phone as people evacuated from office building gather in Reforma Avenue after an earthquake in Mexico City. (Photo / AP)
In that tragedy, too, ordinary citizens played a crucial role in rescue efforts that overwhelmed officials.
Market stall vendor Edith Lopez, 25, said she was in a taxi a few blocks away when the quake struck. She said she saw glass bursting out of the windows of some buildings. She was anxiously trying to locate her children, whom she had left in the care of her disabled mother.
Pictures fell from office building walls, objects were shaken off of flat surfaces and computer monitors toppled over. Some people dived for cover under desks. Local media broadcast video of whitecap waves churning the city's normally placid canals of Xochimilco as boats bobbed up and down.
Witness video shows buildings collapsed in the Mexico City region after powerful earthquake, damage assessment underway pic.twitter.com/abLzcPqpWG— Breaking911 (@Breaking911) September 19, 2017
Mexico City's international airport suspended operations and was checking for damage.
In the Roma neighbourhood, which was struck hard by the 1985 quake, piles of stucco and brick fallen from building facades littered the streets. At least one large parking structure collapsed. Two men calmed a woman seated on a stool in the street, blood trickling form a small wound on her knee.
Much of Mexico City is built on former lake bed, and the soil can amplify the effects of earthquakes centred hundreds of miles away.
Mexico City Following Major 7.1 Magnitude Earthquake pic.twitter.com/fHu3Bsbefm— Breaking911 Nature (@B911Nature) September 19, 2017
The new quake appears to be unrelated to the magnitude 8.1 temblor that hit Sept. 7 off Mexico's southern coast and which also was felt strongly in the capital.
U.S. Geological Survey seismologist Paul Earle noted that the epicentres of the two quakes are 400 miles (650 kilometers) apart and most aftershocks are within 100 kilometers.
There have been 19 earthquakes of magnitude 6.5 or larger within 250 kilometers of Tuesday's quake in the past century, Earle said.
Earth usually has about 15 to 20 earthquakes this size or larger each year, Earle said.
Initial calculations show that more than 30 million people would have felt moderate shaking from Tuesday's quake. The US Geological Survey predicts "significant casualty and damage are likely and the disaster is potentially widespread."