The navy said it was searching for any survivors from the crash, which occurred in the north-central state of Queretaro.

The MI-17 helicopter, which took off from Valle Verde in the neighboring state of San Luis Potosi, was carrying a helibucket with 2,500 liters of water to fight the fire, the navy said in a statement, without giving further details of the accident.

"We hope with all our hearts to find them alive," President Andres Manuel Lopez Obrador said during a political rally in San Luis Potosi.

He said authorities have not been able to reach the accident site because "it is very difficult terrain."

Central Mexico has suffered hundreds of wildfires in recent months due to low rainfall and high temperatures.

A lack of wind and rain have prevented the smoke from dissipating, which worsened the air quality of the capital Mexico City to such an extent that authorities last week declared an environmental alert and warned residents to avoid physical activity outdoors.