A Mexican Navy helicopter with five crew members aboard crashed Friday in a mountainous area while carrying water to help fight forest fires, The Associated Press reported.

The Navy said rescuers were searching for the crew of the Russian-made MI-17 transport helicopter, and it was not clear if any had survived.

Mexico’s north-central state of Queretaro has been using helicopters to help fight a series of forest fires in the pine-covered mountains known as the Sierra Gorda. The chopper was carrying a 660 gallon (2,500 liter) helicopter bucket filled with water when it went down.

The crash occurred in the township of Jalpan de la Sierra, located on a high mountain range.