A powerful earthquake has jolted Mexico City - measuring magnitude 7.1 according to the US Geological Survey (USGS) - causing buildings to sway sickeningly on the anniversary of a 1985 quake that did major damage to the capital. The quake caused rubble to fall onto cars, and some building facades to collapse to the streets.

The extent of damage or injuries was not immediately clear, but people fled office buildings along the central Reforma Avenue. Local media reported at least 49 deaths, and an unspecified number of others who may be trapped in buildings throughout the city.

Mexico's seismological agency estimated its preliminary magnitude at 6.8 and said its centre was east of the city in the state of Puebla. That municipality is about 40 miles southeast of the capital.

One visitor to the city, who asked to be identified simply as Juan, was in a penthouse building in the city when the quake struck. He sent The Independent a text which said: "One word: apocalyptic. We heard the earth roar and the buildings creak. My heart was still pounding fast, minutes afterwards."

Pictures fell from walls and objects were shaken off of flat surfaces. Some people dove for cover under desks.

Mexico City earthquake in pictures Show all 13 1 /13 Mexico City earthquake in pictures Mexico City earthquake in pictures A handout picture provided by the citizen Edgar Cabalceta shows a general view of Mexico City following a magnitude 7.1 earthquake, in Mexico City, Mexico EPA Mexico City earthquake in pictures Rescuers and residents look for victims amid the ruins of a building knocked down by a magnitude 7.1 earthquake that jolted central Mexico damaging buildings, knocking out power and causing alarm throughout the capital on September 19, 2017 in Mexico City, Mexico. The earthquake comes 32 years after a magnitude-8.0 earthquake hit on September 19, 1985 Getty Images Mexico City earthquake in pictures A police officer stands guard near a building which collapsed after a quake rattled Mexico City RONALDO SCHEMIDT/AFP/Getty Images Mexico City earthquake in pictures Rescuers, firefighters, policemen, soldiers and volunteers remove rubble and debris from a flattened building in search of survivors after a powerful quake in Mexico City AFP/Getty Images Mexico City earthquake in pictures Rescuers and residents look for victims amid the ruins of a building knocked down by a magnitude 7.1 earthquake that jolted central Mexico damaging buildings, knocking out power and causing alarm throughout the capital on September 19, 2017 in Mexico City Getty Images Mexico City earthquake in pictures People try to rescue survivors from a collapsed buildings after a magnitude 7.1 earthquake on the Richter scale in Mexico City, Mexico, 19 September 2017. At least 79 people lost their lives in the states of Morelos, Puebla and Mexico by the earthquake of magnitude 7.1 on the Richter scale. EPA Mexico City earthquake in pictures People clear rubble after an earthquake hit Mexico City, Mexico REUTERS Mexico City earthquake in pictures People clear rubble after an earthquake hit Mexico City, Mexico REUTERS Mexico City earthquake in pictures Rescuers and residents assists an injured victim amid the ruins of a building knocked down by a magnitude 7.1 earthquake that jolted central Mexico damaging buildings, knocking out power and causing alarm throughout the capital on September 19, 2017 in Mexico City, Mexico. The earthquake comes 32 years after a magnitude-8.0 earthquake hit on September 19, 1985. Getty Images Mexico City earthquake in pictures People remove debris outside a collapsed building after an earthquake in Mexico City, Mexico REUTERS Mexico City earthquake in pictures People remove debris as they search for possible victims after a quake rattled Mexico City on September 19, 2017. A powerful earthquake shook Mexico City on Tuesday, causing panic among the megalopolis' 20 million inhabitants on the 32nd anniversary of a devastating 1985 quake. The US Geological Survey put the quake's magnitude at 7.1 while Mexico's Seismological Institute said it measured 6.8 on its scale. The institute said the quake's epicenter was seven kilometers west of Chiautla de Tapia, in the neighboring state of Puebla. AFP/Getty Images Mexico City earthquake in pictures A security guard walks over debris of a building which collapsed during a quake in Mexico City AFP/Getty Mexico City earthquake in pictures Reconstruction work in the towns affected by the telic movement has begun. Several temples suffered severe damage. Rex

A video that appears to show the earthquake in action shows lights swaying above people crowding into hallways for safety, and then those lights seeming to lose power.

Another video, streamed live on Twitter's Periscope in the Federal District of the city, showed dozens of men attempting to remove large metal beams that appeared to have fallen during the earthquake - it was not clear what was underneat. A car in the footage was covered in dust, another was smashed, and rubble was strewn all about.

Mexican minister to China Jorge Guajardo tweeted a video showing a building that had collapsed, with rubble covering the sidewalk below. "Panic and frustration after Mexico City earthquake," Mr Guajardo wrote alongside the video.

Yet another posted by Mr Guajardo showed the facade of a what appears to be a 10 story building losing its facade.

The earthquake hits less than two weeks after a devastating 8.1 magnitude trembler that impacted off the coast of Chiapas. That event killed at least 98 people, and left devastation primarily in the souther Mexican states of Chiapas and Oaxaca. All told, those two states have a combined population of nine million people, and are impoverished.

The USGS estimated that there were at least six aftershocks exceeding a 5.0 magnitude after that quake earlier this month. An estimated 1.85 million homes lost power after the initial shock wave, but 74 per cent of those homes saw services restored within hours. The earthquake was the most powerful that Mexico has seen in at least a century.