Four men wearing hoods and masks used a crowbar to break in through the front door just 45 minutes after staff left the premises after the restaurant's first full day of trading.
The gang took the safe which was later found abandoned at Sunderland Point.
Around Â£8,500 had been taken. The thieves had left behind just Â£122 in coins.
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CCTV footage showed the culprits spraying a fire extinguisher on the floor near the takeaway's counter in an attempt to remove their footprints before leaving.
It also showed one of the burglars adjusting a CCTV camera in an attempt to avoid being filmed.
The break-in occurred at around 1.15am on Sunday and the gang were in the shop for just under 10 minutes.
Staff had left the restaurant at around 12.30am. The alarm was not set as workers were due back in just a few hours later.
Police are investigating the crime. Anyone with information who can help their enquiries should contact 101 or the confidential Crimestoppers line on 0800 555111.
The new Burger King next door to the Arndale Centre opened to the public for the first time on Friday afternoon.
Its official opening ceremony was held on Saturday at 10am by the mayor of Lancaster, Councillor Robert Redfern.
A spokesman for franchise operators CPL Food Group, who run 32 Burger Kings nationwide, described Saturday's day of trading in Morecambe as their second busiest opening day ever.
The restaurant closed briefly on Sunday but had reopened again by teatime.