Teenagers were seen performing dangerous jumps into the ocean at Sally Port amid sweltering heat on Monday afternoon.
And despite the weather expected to cool over the coming days, the temperature is still set to remain warm – raising the possibility of more tombstoning incidents.
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However, Portsmouth City Council has pointed out there are a number of dangers when taking part in the dare-devil activity.
Councillor Ben Dowling, member for culture, leisure and economic development, said: ‘We strongly condemn tombstoning from our seafronts and ask that people seriously consider the potential life-changing or even fatal consequences one wrong jump can have for you and your loved ones.
‘The sea may look inviting but jumping from a great height risks shallow waters, submerged objects, serious shock from cold water and strong currents that can make swimming or getting out of the water impossible.’