(CNN) -- Two Indian air force helicopters crashed in the western part of the country Thursday, killing all nine personnel on board, authorities said.
An Indian air force statement said both choppers were on a routine flight in Gujarat state when they crashed.
"A mid-air collision could be one of the causes. But an inquiry has been ordered to investigate," air force spokesman Gerard Galway told CNN.
The two Mi-17 helicopters had taken off from Jamnagar air base, the air force said.
CNN's Harmeet Singh contributed to this report.