A 6.4 magnitude earthquake shook southern Mexico's Guerrero state Thursday, less than a month after a stronger temblor hit the area, the U.S. Geological Survey said.

Thursday's quake, centered about 60 miles northwest of Acapulco and 172 miles southwest of Mexico City, happened at noon local time (1 p.m. ET), the USGS said.

No reports of major damage were immediately made. All city services in Mexico City were working normally after the quake, Mayor Miguel Angel Mancera told CNN affiliate Foro TV.

The USGS preliminarily said the quake's magnitude was 6.8, but lowered the number in the afternoon.