Three crews were scrambled from the fire stations at Kington, Presteigne and Knighton on Monday to deal with a blaze at a farm in Cascob, near Presteigne.
Kington Fire Station later posted on their Facebook page: "Last night we were alerted to assist our "over border" colleagues from Knighton Fire Station and Presteigne Fire Station with an agricultural building fire.
"On arrival the building was well alight from end to end, luckily there was a handy brook running across the drive so we had as much water as we could use, so crews wearing breathing apparatus, ground monitors and jets were used to quickly extinguish the flames meaning crews could back to bed for a few hours sleep before work in the morning! Great work by all."
A spokesperson from Hereford & Worcester Fire and Rescue Service said they assisted colleagues from Mid and West Wales Fire and Rescue Service at the incident that started at 10.44pm.
"A barn, around 30m x 30m, was well alight with the fire fought using four hose reel jets and two main jets, supported by two light portable pumps set into open water.
"Six firefighters used breathing apparatus and a thermal imaging camera was also deployed.
"All persons and animals were accounted for and the incident was marked as pending closure at 01:40."