Staff at Tesco Broadbridge Heath are handing out water to drivers trapped in the car park.
The motorists have been left stranded as traffic chaos brought the road to a standstill.
Irate drivers blamed the Broadbridge Heath bypass works and extra cars using the estate for a sports event at The Bridge Leisure Centre.
Roger Blay, who is caught up in the gridlock, fumed: “It’s disgusting the way that they have done this. You can’t get in or out it’s gridlocked. You just cant move [or] get out of the car park.”
He said that staff were handing out bottles of water to help drivers cope with the heat.
Roger added: “It’s awful. We have been sat there for an hour in the car not moving. Everything’s gridlocked - it’s appalling.
“People are going to be stuck in here for hours on end.
“Everybody is hot. The point is you don’t want to be sat in Tesco’s car park for five or six hours.
“There’s a complete lack of consideration for the motorist.
“There’s literally thousands of cars here at a standstill.”
But Roger’s not the only driver to vent his frustration.
On the County Times Facebook page Lorinda Greatorex said: “Diabolical - I’m trapped in Tesco carpark now some people have been waiting an hour and still no movement, lots of very young children crying because of heat.”
Geoff Oborne added: “Been trying to get out since 12.10pm. It’s now 1.16pm and I’m still in the car park.... It’s gridlock.
“Cars going the wrong way, cars reversing out at the Tesco roundabout. It’s simply mad.”
Tesco and West Sussex County Council have been approached for comment.