A 5.5-magnitude earthquake shook the state of Oaxaca in southern Mexico on Tuesday, but there were no immediate reports of damage, officials said.

The quake was felt in the historic center of the state capital, also called Oaxaca, a colonial city of 300,000 people, but with low intensity, said an AFP correspondent.

Governor Gabino Cue said on Twitter that officials have "activated the seismic alarm system" in preparation for any further quakes or aftershocks.

The National Seismological Service said the epicenter was 23 kilometers (14 miles) northwest of the town of Matias Romero, some 670 kilometers from Mexico City.

Unlike past earthquakes in the south, this one was barely felt in the capital.