A military helicopter carrying officials assessing damage from a powerful earthquake has crashed in southern Mexico, killing 13 people and injuring 15, all of them on the ground.

The Oaxaca state prosecutor's office said in a statement that five women, four men and three children were killed at the crash site and another person died later in hospital.

Jorge Rosales, a local reporter who was aboard the helicopter when it crashed, described harrowing moments as the pilot lost control and the helicopter attempted to land in a swirl of dust.

"The moment the helicopter touched down it lost control, it slid - like it skidded - and it hit some vehicles that were stationed in the area," he said.

"In that moment, you couldn't see anything, nothing else was heard beside the sound that iron makes when it scrapes the earth."

Mexico's Interior Department said that the helicopter was carrying Secretary Alfonso Navarrete and Oaxaca state Governor Alejandro Murat, who were evaluating reports of damage from the powerful 7.2 magnitude earthquake, before their helicopter crashed.

The helicopter was attempting to land on a vacant lot in the city of Jamiltepec, about 19 miles from the area of Pinotepa Nacional, the Mexican army said.

The US Geological Survey originally put the magnitude of Friday's quake at 7.5 but later lowered it to 7.2. It said the epicentre was 33 miles north-east of Pinotepa in southern Oaxaca state, and had a depth of 15 miles.

President Enrique Pena Nieto said via Twitter that both officials and crew were unhurt, although the interior department said that they had light injuries.

PA Media