Police believe the thieves twice broke into the shop in Station Street, Seymour, on May 24 and May 26 between 1am and 8am, by removing the glass sliding door. Once inside, they stole a Lego stand valued at $10,000 before fleeing in a car.

The second burglary occurred between 1pm on Sunday and 7am on Monday.

The thieves once again removed the front glass door, and nicked a further $5000 of Lego, targeting the Lego "City" and Lego "Technic" sets.

Owner of Seymour Toyworld, Werner Baumann, said the robbers were a highly organised and professional group targeting toy stores for Lego. 

‘‘These people are very smart in what they’re doing,’’ he said.

‘‘They understand how business works and how to break into places without leaving any evidence.’’

Mr Baumann said the thieves were ‘‘absolutely not locals’’, and that several other Toyworld franchises had also been robbed this year.

‘‘They robbed the Fawkner Toyworld the day before mine and before that, the shop in Benalla,’’ Mr Baumann told Fairfax Media.

The shocked owner said the offenders had stolen most of his Lego stock, leaving the country store with only 10 per cent ‘‘of what I usually have’’.

‘‘It will seriously impact my business, because Lego is a very good seller,’’ he said.

Mr Baumann said the stolen Lego would most likely be put on eBay or sold at Melbourne markets in increments so that thieves would avoid detection.

‘‘It won’t all go out in one hit - it’s quite difficult to track down once it’s gone.’’

He said he hoped media attention would encourage people to speak out about the heist.

‘‘It doesn’t feel very good to have people invade your personal space,’’ he said. ‘‘These people need to be caught.’’

Detective Senior Constable Ian Potter told radio station 3AW he also suspected the Lego was being sold online or at markets in Melbourne.

‘‘[It’s important] that the public are aware of any market or market stalls that are selling Lego, in particular the Lego ‘Technic’ brand and the Lego ‘City’ brand,’’ he said.

Victoria Police spokeswoman Senior Constable Melissa Seach said police were keen to speak to any witnesses to the break-in.

Anyone with information is asked to phone Crime Stoppers on 1800 333 000.