A magnitude 7.6 earthquake struck western Mexico on Monday on the anniversary of two devastating temblors, killing at least two people, damaging buildings, knocking out power and sending residents of Mexico City scrambling outside for safety.

Two died in the Pacific port of Manzanillo, authorities said, one crushed by the facade of a department store while another was found dead at a mall. Videos on social media showed the roof of the mall collapsed into the top floor, a gym, as people yelled for help.

Authorities also reported damage to several hospitals in the western state of Michoacan near the epicentre, which was in a sparsely populated part of Mexico. One person was injured by the falling glass at one of the hospitals, the government said.

The quake hit shortly after 1pm (1800 GMT) near Mexico's west coast and close to Michoacan's border with the state of Colima - where major port Manzanillo is located, the US Geological Survey (USGS) said.

It was relatively shallow, at only 15km deep, which would have amplified its impact.

The US Pacific Tsunami Warning Centre issued a tsunami warning for coastal areas, saying waves reaching one to three metres above the tide level were possible.

Mexico City Mayor Claudia Sheinbaum said there were no immediate reports of major damage in the capital after the quake struck, which rumbled through Mexico on the same day as destructive earthquakes battered the country in 1985 and 2017.

"It seems like a curse," Isa Montes, a 34-year-old graphic designer in the city's central Roma neighbourhood, said of the quake's timing as helicopters flew overhead, surveying the city.

The National Autonomous University of Mexico, one of the country's most prestigious seats of higher learning, said there was no scientific explanation for three major quakes on the same day and attributed it to pure coincidence.

But others could not quite believe it.

"It's this date. There's something about the 19th," said Ernesto Lanzetta, a business owner in the Cuauhtemoc borough of the city. "The 19th is a day to be feared."

Thousands of people were killed in the Sept 19, 1985 earthquake and more than 350 died in the Sept 19, 2017 quake.

Many Mexicans reacted to the latest quake by posting an array of memes online venting their anxiety and finding humour in the natural disaster.

President Andres Manuel Lopez Obrador also noted material damage near the epicentre. Images posted on social media showed buildings badly damaged.

Mexican authorities said the seismic alert had sounded nearly two minutes before the quake struck, giving residents time to evacuate.

Still, some people in the capital struggled to grasp it was a real quake as the government had already sounded the alarm earlier in the day as a practice exercise commemorating the past earthquakes on the same day.

Power out

In Coalcoman, Michoacan, not far from the epicentre, pictures showed shingles knocked off homes and building walls cracked by the force of the quake. In one store, the merchandise was scattered across the floor.

Power was knocked out in parts of the trendy Roma neighbourhood in Mexico City, some 400km from the epicentre. The national power utility said outages hit 1.2 million users.

Roma residents stood on the streets cradling pets, while tourists visiting a local market with a guide were visibly confused and upset. Traffic lights stopped working, and people clutched their phones, sending text messages or waiting for calls to get through.

Clara Ferri, who owns an Italian bookshop in Roma, said she told a customer to get out as soon as she heard the windows rattle, her senses attuned to the sounds of incipient earthquakes after 16 years in the location.

"It was like the dentist's drill for me," she said.

The rumbling grew in intensity, and as Ferri gathered with neighbours at an intersection, she looked up to see the eight-story building that houses her shop sway from side to side.

When she returned, shelves had toppled like dominos, sending over 1,000 books into heaps on the floor.

Officials roped off the sidewalk, which was littered with masonry that appeared to have fallen off the building. Residents trickled out with pets and suitcases, preparing to spend the night elsewhere, and a woman carefully escorted her 89-year-old uncle in his blue-and-white striped pyjamas.

- Reuters