VANCOUVER -- Vancouver police said Friday they’ve had six reports in the last week of people receiving prank calls in which they heard a recording of a woman in distress.

Police said the calls have come from international area codes, but so far, the motive behind them is not clear.

Vancouver police said they are looking into the calls but that it's very difficult to trace their origin.

Mikala Folb said she received one of the calls while she was at work around 9 a.m. on Thursday. The call appeared to be coming from a U.K. number, a place where she used to live and still has many friends, so she picked up the phone, even though she didn't recognize the number.

"I instantly heard the sound of a woman frantic, sobbing sort of sad screaming. Not quiet-crying but sort of hysterical," she said. "I completely froze. I was standing there surrounded by my colleagues and they could hear it through the phone."

WARNING: This audio may be disturbing for some listeners. Mikala Folb's phone recorded part of a distressing call she received on Thursday where a woman can be heard screaming.

Folb then asked the caller who they were and heard what sounded like "it's me," in response to her question. She said shortly after that, the call disconnected but left her "chilled to the bone."

"Logic dictated, I'm sure this is a prank," she said. "But this was unlike anything we’ve heard. There was no payoff…it sounded like someone was being kidnapped or brutally hurt."

Folb said the tone of the call was so concerning, she decided to text the number back to ask the caller if they were alright. She had also lost a lot of numbers in a recent phone update, so she was concerned the caller was someone she might actually know.

"I said, 'Who is this? I don't have your number. Are you ok? Clearly you're not,'" she said. She also tried phoning the person back, but the call failed. Folb said she didn't understand the caller's motivation, other than perhaps figuring out that her number is in service.

"You're tempted at first to just dismiss it but it was too chilling," she said. "You didn't want to be the person who didn't do something if it was real."

Folb eventually phoned the VPD's non-emergency line to report the call and was told police had started getting reports about similar calls a few days earlier.

"We are asking the public to be vigilant. If they aren't expecting a call from an unknown number, don't answer it," said Const. Tania Visintin in a statement. "If anyone does truly believe someone could be in danger, please call 911 immediately."