Ernest Jones Jewellers and the Wallis/Miss Selfridge store are both crime scenes as staff arrived to find the shutters forced open and windows smashed.
What appears to be an organised gang set a fire in the rear car park to the Cascades before using sledgehammers to smash their way into the outlets at 3am.
The entrance doors to the Cascades, situated between both shops, also suffered serious damage.
Police are appealing to any witnesses to call 101 immediately.
Stores in Portsmouth's Cascades Centre are cleaning-up after multiple break-ins over night.
Alternatively you can contact the Crimestoppers charity anonymously on 0800 555 111 or via: