Fruit thieves are on the prowl in northern Australia, but Northern Territory mango farmers are going to extraordinary lengths to protect their crops.

Tom Harbrow, who owns Pine Creek mango plantation 200 kilometres south of Darwin, has for the first time installed security cameras and hired security guards to protect the fruit dangling on his 6200 trees.

"It's worthwhile doing it in a year like this when they're so valuable," he said. "The season has been disastrous for some growers, they're only getting half or a third of what they'd expected. We got about 70 per cent, so we're pretty lucky."

Ramping up security and fortifying fences on his 100-hectare property cost him "a few thousand dollars" this month. But it was a small price to pay, he said. Two years ago thieves drove off with two tonnes of early season fruit worth $20,000.

Mr Harbrow is selling mangoes for $70 to $80 per seven kilogram tray, at the wholesale level, with consumers forking out $100 a tray, or $5 a mango.

Trevor Dunmall, chief executive of the Australian Mango Industry Association, said in an ordinary year, a tray of early pickings would fetch $45 to $50 at wholesale. "Before the Northern Territory production became large, there was often fruit theft in Burdekin [a region in north Queensland]. People came along, jumped out of vans and stripped the trees close to the road," he said. "It has certainly been an issue in recent years and police have increased their vigilance."

Ross Maxwell, a tropical fruit grower from Jabiru Orchards near Darwin, said he has heard of other farmers installing CCTV cameras.

He once caught thieves loading up crates with his fruit. "It happens more now than it did in the past," he said.