MEXICO CITY (AP) — A Mexican Navy helicopter with five crew members aboard crashed Friday in a mountainous area while carrying water to help fight forest fires.

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.

President Andrés Manuel López Obrador wrote in a Tweet that “we hope with all our hearts that these five public servants are alive.”

The 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 that drops abruptly onto Mexico’s Gulf coast plain.

Mexico has suffered hundreds of brush, pasture and forest fires in recent weeks amid very hot, dry conditions.