A man suspected of threatening a Melbourne animal shelter worker with an assault rifle and demanding to know "where the cats were" is being interviewed by police.
Detectives were talking to the 44-year-old from Langwarrin on Tuesday afternoon following allegations a man approached the on-call ranger in the car park of The Lost Dogs' Home at Cranbourne West, southeast of Melbourne, late Monday evening.
Senior Sergeant Glen Cruse told reporters on Tuesday morning the ranger wound down the window of her vehicle, thinking the man was an officer as he was dressed in tactical-style camouflage clothing with a mask and helmet.
He then walked her into the shelter at gunpoint, tied her hands with cable ties and asked "where the cats were" before leaving without taking anything.
"The circumstances are a little bizarre," Sgt Cruse said.
"But it's really concerning (he) has confronted someone like that in the middle of the night, dressed the way he was and armed with a firearm."
"He threatened to use the firearm on her if she didn't comply."
The woman, in her early 20s, was able to free herself and raise the alarm.
She didn't suffer any injuries but was 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 in a statement to AAP.
"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."
The home said no animals were harmed.
Fellow animal welfare group RSPCA Victoria has reached out to The Lost Dogs' Home to offer support.
"We are thinking of them and their animals," chief executive Dr Liz Walker told AAP.
The man's motivations remain unknown but appear to be linked to a desire to rescue animals.
His tone was described as "assertive and deliberate" without being "overly aggressive".
"He was asking about where the cats were stored and talking about (how) a lot of animals are killed," Sgt Cruse said.
"(He) seems to have the belief that potentially animals are treated in a cruel way and killed on the premises.
"We're looking at all motivations and possible scenarios."
There was no indication the pair were known to each other or that any other witnesses were present, Sgt Cruse added.
He also assured the community it was safe, despite the man - described as Caucasian, at least 1.83m tall and solidly-built - being unknown to police.