A newly opened shopping mall on Mexico City's south side partly collapsed Thursday after structural problems led the mall's operators to quickly evacuate the area, and no injuries were reported.
Officials said a support beam failed in a cantilevered office area on the top floors that stuck out from the main mall building.
Restaurant worker Juan Ramon Hernandez said people in the mall were evacuated only about five minutes before the offices sheared off.
"We heard a big noise and they began to evacuate us from the plaza," said Hernandez. "About five minutes later was when the collapse happened."
Videos posted on social media showed the multi-story section collapse in a cloud of dust and twisted metal. Some of it fell into lanes of a major freeway, which had been closed shortly before the collapse.
The Artz Pedregal mall opened in March, though parts remain under construction. It had drawn the ire of neighbors worried about the loss of open space, congestion and other issues. Built on the edge of the city's main expressway, the mall had suffered previous subsoil slides.
Mexico City Mayor Jose Ramon Amieva said the collapse occurred in an area of offices, and experts were investigating whether the collapse of the cantilevered area was due to structural defects or soil settling.
"They noticed that a separation was occurring" between the overhang and the rest of the building hours before the failure, Amieva said.
Calling it a "case of negligence," the mayor said the mall's construction permits and other authorisations should be reviewed as investigators try to find out what happened.
In a statement, the mall's operator said it notified city authorities when it noticed signs the area was collapsing. It said it regretted the impact the accident was having on traffic on the notoriously crowded Periferico expressway. At least two lanes were closed.
The mall was controversial in part because it threatened to clog traffic, and because it was built near a rain catchment basin that serves to regulate the city's seasonally heavy rainfall.
The risk posed by substandard building has been a longstanding issue in Mexico City, where many poorly built or designed buildings collapsed in the city's 1985 and 2017 earthquakes.
The city also has notoriously bad subsoil conditions, and developers often build on unstable land.
In 2016, while foundation work was still being done on the mall, a retaining wall next to the expressway partly collapsed.