Photo: Contributed

UPDATE 9:19 p.m.

Crowds gathered on Mexico City's central Reforma Avenue as well as on streets in Oaxaca state's capital, nearer the quake's epicenter, which was in a rural area close to Mexico's Pacific coast and the border with Guerrero state. There were no immediate reports of deaths.

"It was awful," said Mercedes Rojas Huerta, 57, who was sitting on a bench outside her home in Mexico City's trendy Condesa district, too frightened to go back inside. "It started to shake; the cars were going here and there. What do I do?"

She said she was still scared thinking of the Sept. 19 earthquake that caused 228 deaths in the capital and 141 more in nearby states. Many buildings in Mexico City are still damaged from that quake.

The U.S. Geological Survey originally put the magnitude of Friday's quake at 7.5 but later lowered it to 7.2. It said the epicenter was 33 miles (53 kilometres) northeast of Pinotepa in southern Oaxaca state. It had a depth of 15 miles (24 kilometres).

UPDATE 5:57 p.m.

About an hour after the quake, a magnitude 5.8 aftershock centred southern Mexico caused tall buildings in Mexico City to briefly sway again.

USGS seismologist Paul Earle said Friday's earthquake appeared to be a separate temblor, rather than an aftershock.

A Sept. 7 quake killed nearly 100 people in Oaxaca and neighbouring Chiapas, but was centred about 273 miles (440 kilometres) southwest of Friday's earthquake, Earle said.

In Mexico's capital, frightened residents flooded into the streets in Condesa, including one unidentified woman wrapped in just a towel, but there were no immediate signs of damage.

"I'm scared," said Rojas Huerta, recalling five months ago when buildings fell as she ran barefoot into the street. "The house is old."

ORIGINAL 4:13 p.m.

A powerful earthquake shook south and central Mexico Friday, causing people to flee buildings and office towers in the country's capital, and setting off quake alert systems.

Crowds of people gathered on central Reforma Avenue in Mexico City as the ground shook.

The U.S. Geological Survey put the quake's preliminary magnitude at 7.2 and said its epicenter was 53 kilometre) northeast of Pinotepa in Oaxaca state. It had a depth of 24 km.

The epicenter is a rural area of western Oaxaca state near the Pacific coast and the border with Guerrero state.

The Oaxaca state civil protection agency said via Twitter that it was monitoring the coastline.

A magnitude 7.1 earthquake in central Mexico on Sept. 19 left 228 people dead in the capital and 369 across the region.