A Florida woman failed massively when she got locked in a vault she was trying to burgle.

Fatima Milanovic, 46, tried to steal $6 million worth of diamonds but her plan clearly didn't work out.

"She came here to inspect stones without bringing any tools, no magnifying glass, no diamond dealers loop, nothing, so it was obvious she was about to pull something," owner Vladislav Yampolski said.

Yampolski took Milanovic to the vault to look at jewels where he alleged she kept trying to distract him.

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She allegedly had a replica package with fake stones inside of her bag.

"That's how she tried to scam us," Yampolski said. "She brought her own materials, wrapped it herself with her own tape and tried to pull the switch because she had the identical package in her bag, pre-made."

Yampolski figured out what she was trying to do and shut her in the vault before calling the police.

Police arrested Milanovic on charges of grand theft and organised fraud.