Dressed in a military uniform, the 45-year-old singer joined the 40 remaining hopefuls as they sang Take That’s 2010 hit Kidz.
Dannii marched on and paraded around the contestants yelling phrases intermittently.
“Do you have what it takes to be in this band? Are you strong enough?” she was heard saying.
The performance sparked an online frenzy as viewers took to Twitter to give their verdict.
Let It Shine: Dannii Minogue led the opening performance tonight with mixed reviews from viewers
Let It Shine: Dannii was dressed as a military officer as she yelled at the contestants
One social media user said: “Dannii's presence during this whole thing is really cringe and fairly disturbing #LetItShine.”
“Danni Minogue couldn't have been more cringey if she tried! #letitshine,” another agreed.
A third urged: “Danni, please stop. This is actually terrifying! Who decided that this would happen?! #letitshine.”
Let It Shine: The 45-year-old singer teased fans with a pre-show picture of herself in her uniform
Dannii Minogue: Her SEXIEST music video moments
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The Australian star enjoyed a huge pop career in the 1990s and 2000s before becoming a top telly judge.
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Dannii's All I Wanna Do is one of her best-known hits
While a fourth was confused, writing: “Only just catching up with #LetItShine. Why is Dannii dressed like a Prussian military skeleton?”
However, one fan enjoyed the number, tweeting: “Really enjoying the opening of @BBCLetItShine – quite like military Dannii #LetItShine.”
Let It Shine continues next Saturday at 6.55pm on BBC One.