A magnitude 6.1 earthquake has shaken southern Mexico and rattled buildings as far as 400km away in Mexico City.

So far there have been no reports of damage or injuries.

The epicentre of the earthquake was 18km northwest of the town of Ayutla de los Libres in the southern state of Guerrero, according to the United States Geological Survey (USGS).

The USGS revised down an initial reading of 6.4.

The USGS also said the tremor struck at a depth of 34.8km. A 5.3 magnitude aftershock hit near the popular Pacific coast tourist resort of Acapulco half an hour later.

Buildings swayed for around a minute in Mexico City after the first quake, and several offices in the capital evacuated staff. The quake struck at the height of the morning rush-hour.

Mexico City Mayor Miguel Angel Mancera said on Twitter that there were no reports of injuries or damage in the capital.

No damage was reported in the state of Guerrero either, although local governor Angel Aguirre Rivero said on Twitter that emergency services were checking buildings in locations including Acapulco following the aftershock.