A man is assisting police with their inquiries after a Melbourne animal shelter worker was threatened by a man in military-style clothing wielding an assault rifle, who demanded to know “where the cats were”, police allege.

They say the alleged offender, who was dressed in “tactical style camouflage clothing”, including a mask and helmet, approached the on-call ranger in the car park of the Lost Dogs’ Home at Cranbourne West, south-east of Melbourne, about 10.20pm on Monday.

Senior Sergeant Glen Cruse said the ranger wound down the window of her vehicle, thinking the man was an officer.

He then walked her into the shelter at gunpoint, tied her hands with cable ties, demanded to know “where the cats were” before leaving without taking anything.

Late on Tuesday afternoon, police said a 44-year-old man from nearby Langwarrin was being questioned about the incident.

“The circumstances are a little bizarre but it’s really concerning [he] has [allegedly] confronted someone like that in the middle of the night, dressed the way he was and armed with a firearm,” Sergeant Cruse said.

“He threatened to use the firearm on her if she didn’t comply.”

The woman, in her 20s, was able to free herself and raise the alarm.

Sergeant Cruse said she was unhurt, but had been left shaken.

“It’s very traumatising to be confronted like that in a dark, remote location,” he said.

“What she’s gone through and … how she was able to deal with the situation and communicate with the offender and notify police – it’s very brave.”

The incident has left the Lost Dogs’ Home “shocked and extremely concerned”, with the company thanking the community for the outpouring of support for its staff.

“The home has a zero-tolerance policy when it comes to violence against our staff in any shape or form,” it said.

“Our main priority is the welfare of our staff and we are providing all the support possible to the animal transport team member who was a victim in this horrendous ordeal.”

It is aiding Victoria Police’s efforts to catch the armed man and confirmed no animals were harmed.

-AAP