The Etihad crew chose to make the landing with 349 people onboard at about 5:30am AEDT.
Etihad said a warning light came on in the cockpit.
"Etihad Airways flight EY450 … diverted to Adelaide Airport following a technical fault with a cargo-hold air-recirculation fan," a statement said.
"Due to crew rest requirements, Etihad is assisting guests to their ultimate destination on other airlines.
The airline said it had now been forced to cancel another flight because of the incident.
"Additionally flight EY451 from Sydney to Abu Dhabi has been cancelled. Guests who have been booked on the flight will be rebooked on later Etihad Airways services out of Sydney.
"Etihad Airways apologises for the inconvenience."
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