The alarms went off at Portfield Retail Park, near Chichester, and emergency services have evacuated Currys, John Lewis and Marks and Spencer as a precaution.
A spokesperson for West Sussex Fire and Rescue said officers and one crew from Chichester Fire Station are on the scene, carrying out an investigation.
"Other premises at the site are still operating as usual, but would urge people to avoid the area at this time if their journey is not essential,” they added.
1. Suspected gas leak in West Sussex retail park
West Sussex Fire and Rescue is leading the way, and has a team conducting an inspection of the evacuated sites. Photo: Eddie Mitchell
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Photo: Bex Bastable Photo: Bex Bastable
3. Suspected gas leak at West Sussex Retail Park
Several shops have been evacuated Photo: Eddie Mitchell
4. Suspected gas leak at West Sussex Retail Park
John Lewis, M&S Foodhall and Currys have been taped off and evacuated as a precaution Photo: Eddie Mitchell