A Fire and Emergency NZ spokesman said two crews from the Lake Tekapo and four helicopters with monsoon buckets were on the ground at the Tekapo Military Training Area tackling the large vegetation fire.
The blaze was reported at 11.23am today.
State Highway 8 was not affected and remained open for now, the spokesman said.
Tekapo resident George Empson was near the military base taking photos of wildlife when he heard one loud explosion, followed by a second.
‘‘While I was leaving I had to open a gate to get the truck through . . . when I looked up to the west that’s when I saw this massive smoke cloud.’’
Mr Empson could still see smoke coming up from the site.
‘‘From time to time they come to the base to explode old ammunition — whenever they’re live firing they put up a red flag which was flying today.’’
A New Zealand Defence Force spokesperson said nobody was hurt in the fire which broke out following planned ammunition disposal.
Extra NZDF resources were going to Tekapo to support the response.