A 7.6 magnitude earthquake shook Mexico's central Pacific coast on Monday, setting off a seismic alarm in the rattled capital on the anniversary of two earlier devastating quakes.

There were no immediate reports of significant damage from the quake that hit at 1:05 pm local time, according to the US Geologic Survey, which had initially put the magnitude at 7.5.

It said the quake was centred 37 km (23 miles) southeast of Aquila near the boundary of Colima and Michoacan states and at a depth of 15.1 km (9.4 miles).

Michoacan's Public Security Department said there were no immediate reports of significant damage in that state beyond some cracks in buildings in the town of Coalcoman.

Mexico's National Civil Defence agency said that the navy's tsunami centre had not issued an alert because due to the epicentre's location, no variation in sea levels was expected. However, that contradicted an alert from the US Tsunami Warning Centre. It said hazardous tsunami waves were possible for coasts within 186 miles (300 km) of the epicentre.

Mexico City Mayor Claudia Sheinbaum also tweeted that there were no reports of damage in the capital

Alarms for the new quake came less than an hour after a quake alarms warbled in a nationwide earthquake simulation marking major, deadly quakes that struck on the same date in 1985 and 2017.

Humberto Garza stood outside a restaurant in Mexico City's Roma neighborhood holding his 3-year son. Like many milling about outside after the earthquake, Garza said that the earthquake alarm sounded so soon after the annual simulation that he was not sure it was real.

I heard the alarm, but it sounded really far away, he said.

Outside the city's environmental ombudsman's office, dozens of employees waited. Some appeared visibly shaken.

Power was out in parts of the city, including stoplights, snarling the capital's already notorious traffic.