The closure has caused severe delays for those travelling to and from the airport.
The roads surrounding the motorway where drivers have been diverted are a complete standstill, according to reports.
Highways England shut the busy motorway this morning to allow UK power networks engineers to repair a damaged overhead power line.
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The works will take a "couple of hours" to complete, according to West Sussex County Council's highways department.
The road is shut northbound between J10 (Crawley) and J8 (M25), and southbound between J8 and J9 (Gatwick) for "safety reasons".
Southbound traffic is advised to follow the hollow diamond symbol, while northbound traffic should follow the solid square diversion symbol.
We appreciate the inconvenience this causes
A spokeswoman from UK Power Networks said: "We appreciate the inconvenience this causes.
"We will complete electrical work as quickly as is safely possible so the road can be reopened.
"We'll be bringing you live updates on the closure, including details on delays and diversion routes."
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