Thousands of residents in Mexico City woke up with quake alarms on Saturday that made people run into the street in their pyjamas, but then nothing happened. Nerves were on edge as a 5.7-magnitude quake had struck south-central parts of the country hours earlier, though there were no reports there of injuries or damage.

Alarms sounded in some of the capital’s central neighbourhoods, including Escandon and Del Valle, sending dozens out of their homes, AFP reported.

Similar scenes were witnessed in the Iztacalco neighbourhood farther south, as well as in Popotla in the city’s east, while in neighbourhoods including Roma and Doctores no alarm was sounded.

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Mexico City Mayor Claudia Sheinbaum initially reported the alarm on Twitter, but minutes later confirmed there had been no quake.

She subsequently said she had instructed officials to investigate why alarms had been sounded.

After Friday’s earthquake, several people reported on social media that the alert was accompanied by a message saying it was a simulation — confusing many about whether to leave home.

The capital’s C5 security command centre said Friday it was investigating the matter.

The capital’s earthquake alert system uses seismic monitors located principally on Mexico’s southern Pacific coast, where most temblors in the region originate.

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It is designed to provide a warning of up to two minutes before a quake is felt in the capital.

Mexico, with its extensive Pacific coast, is subject to numerous quakes.

A 7.1-magnitude temblor on September 19, 2017, caused 370 deaths, primarily in the capital.

On the same date in 1985, a powerful 8.0-magnitude quake shook the capital, leaving more than 10,000 people dead.