Thieves armed with weapons, including a sledgehammer, smashed their way into two Apple stores in Perth before threatening security guards and making off with $300,000 worth of goods, mostly mobile phones.

A group of about six men dressed in dark clothing smashed their way into the Apple store in Perth's CBD about 2:15am on Monday, but were disturbed by a passing taxi and fled empty-handed.

Police said the same group broke into to the Apple store in suburban Booragoon shortly afterwards, threatening security staff before stealing the phones and other goods.

The clean-up process started early on Tuesday. ( ABC News: Jon Kerr )

Two vehicles linked to the robberies were found burnt out and abandoned in Perth's southern suburbs.

Potential buyers beware

Detective Senior Constable Matt Whelan warned people to be careful when purchasing second-hand devices.

"Police want to get the message out to the public that the phones that have been stolen have security on them by the manufacturer," he said.

The thieves also targeted the Hay Street store, but left with nothing. ( ABC News: Jon Kerr )

"The manufacturer knows what phones have been stolen and security measures will be enabled meaning these telephones are useless.

"We want to protect the public and we ask anyone considering buying second-hand or used mobile phones that are slightly cheaper to consider this because ultimately you could be left with something that's useless.

"By supporting or by buying these black-market products, you're ultimately causing these burglaries to occur because you're generating this market where people can buy technology cheap, so that makes this group of people want to do this again."

Repairs have been carried out at the stores. ( ABC News: Jon Kerr )

Police are hoping witnesses will come forward.

"We ask anyone who've witnessed a convoy of cars speeding towards the city or towards Booragoon in the early hours of this morning, or people who were around either of the incident locations who may have witnessed something to come forward to police," he said.