Sussex police have said that the incident happened on the seafront in Worthing today.
An air ambulance landed at the scene.
It comes as the warm weather continues across the south coast.
Thunderstorms in Portsmouth yellow weather warning: The Met Office forecast for the next three days in city, Fareham, Gosport, Havant and Waterlooville and Hampshire
Emergency crews battling to save someone’s life on Southsea seafront
Police update on probe into death of ‘Wiggy’ Symes after fatal dog attack in Fareham
Portsmouth Traffic: M27 between junctions 11 and 12 closed throughout August amid footbridge repairs with A27 diversion in place
Southsea seafront incident: Police update after man found 'unresponsive'
Adur and Worthing Police tweeted: ‘Emergency services responded to an incident on Worthing seafront around midday today.
‘A woman, believed to be in her 50s, is reported to have suffered a medical episode and has sadly died.
‘Our thoughts are with her loved ones at this difficult time.’
For all the latest news, traffic and travel, what’s on, Pompey, sport and breaking stories visit The News’s website.
We will be bringing you all of the latest stories from across Portsmouth and surrounding area throughout the day.
If there is a story you think we should know about, you can contact us via our email [email protected] or via our social media channels – Facebook or Twitter.
Do not contact us while you are driving. To stay up to date with all the latest Portsmouth news follow us on twitter @portsmouthnews or like our Facebook page.