Less than one minute into the second quarter, a message was played over the stadium's loudspeakers instructing all patrons to immediately leave the venue.
Umpires stopped the match and players gathered in team huddles in the middle of the ground as confused fans began heading for the exits.
A few minutes later, a second message was played to clarify it was a false alarm.
The MCC released a statement confirming fans were never in serious danger.
"The MCG emergency evacuation system was automatically triggered in a food outlet on level four of the Ponsford Stand," the statement said.
"An investigation into the issue was immediately commenced and no evidence of risk to patrons was detected.
"Venue management was able to stop the evacuation procedure and allow patrons back into the venue after approximately five minutes.
"The MCC sincerely apologises for the inconvenience to patrons and the competing clubs."
Collingwood led the match 5.3 (33) to 1.6 (12) when play was halted.
It restarted with a ball-up in Adelaide's forward line.
This is not the first time a false alarm has shocked MCG patrons.
In 2015, an emergency siren sounded moments before the second half began in a Geelong-Richmond match.
It was caused by a fan's football hitting a sprinkler in the Ponsford Stand.
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