People stand in the street after hearing an earthquake alarm, in Mexico City, Saturday, Sept. 23, 2017.
People stand in the street after hearing an earthquake alarm, in Mexico City, Saturday, Sept. 23, 2017.

A powerful aftershock rocked Mexico on Saturday, triggering new alarms in a country struggling to recover from two recent quakes that together killed nearly 400 people.

The U.S. Geological Survey said the Saturday's quake had a magnitude of 6.1 and was centered in the southern state of Oaxaca, about 360 kilometers (225 miles) southeast of Mexico City, which was still reeling from Tuesday's 7.1 magnitude quake that killed at least 300 people. Three people died during Saturday's tremor.

WATCH: Rescue work continues at quake-damaged building

Officials said Saturday's quake was felt in Mexico City, swaying buildings in the capital. It was not immediately clear whether it caused damage, injuries or deaths.

Mexico's disaster agency said Saturday's quake was an aftershock of the 8.1 quake that hit Mexico's southern coast Sept. 7, killing nearly 100 people.

The Popocatepetl volcano, which is south of Mexico City but can be seen from there on a clear day, sent a column of ash into the sky, capping an intense period of seismic activity.

Rescue workers continued to search through rubble from Tuesday's quake, but were forced to suspend some rescue efforts by the shaking Saturday, according to Mexico's civil protection agency.

The crews, supported by teams from nations around the world, including Israel, Japan and the United States, have rescued at least 60 people in Mexico City and surrounding towns.

On Thursday, the U.S. Agency for International Development sent more than 60 disaster responders and tools and medical equipment to Mexico City.

FILE - Rescue workers, some holding their arms up
Rescue workers, some holding their arms up as a sign to maintain silence, search for survivors at an apartment building at Amsterdam and Laredo streets that collapsed during an earthquake in the Condesa neighborhood of Mexico City, Mexico, Sept. 21, 2017

As of Friday, rescuers were finding more bodies than living survivors, but officials said there were signs of life at some sites picked up by dogs and sensors. The Mexican military said 115 people had been pulled alive from the rubble.

President Enrique Pena Nieto insisted rescue operations would continue. He praised Mexicans' rapid response to the disaster, while stressing the priorities remained saving lives and getting medical attention to those in need.

"I need to recognize the volunteers who are unconditionally helping those who need it," Pena Nieto said.

National Civil Protection Chief Luis Felipe Puente said 155 of the fatalities had occurred in Mexico City. In a tweet Friday, he said the death tolls remained unchanged in other areas, with 73 in the state of Morelos, 45 in Puebla, 13 in Mexico state, six in Guerrero and one in Oaxaca.

While officials remained focused on searching for survivors and caring for those who were injured in Tuesday's temblor, those whose lives were upended were wondering what would happen to them.

About 2,000 homes were damaged in the quake. Many were rendered uninhabitable.

Mexico set up 50 shelters to house quake survivors, but some people were choosing to sleep in the streets, fearing more aftershocks.