A shopping centre flooded just hours after reopening to the public.
Mobile phone footage shared on social media showed a stream of water gushing through The Galleries, in Wigan.
It came after heavy rainfall and thunderstorms struck the region on Monday afternoon.
The shopping centre's Makinson Arcade and Victorian Arcade were among the areas worst affected.
Stephen Pollitt was inside The Galleries at the time. He said: "The water ran down from the Grand Arcade and then down the Makinson Arcade.
"It was running down like a shot and going in the shops.
"They closed the shopping centre while they dealt with it."
A clean-up operation is now under way as managers and traders assess the damage caused by the flash flooding.
Simon Tucker, centre manager at The Galleries, said: "As we carefully emerge from the lockdown we are having to ask our customers for their patience, particularly in these early days whilst everyone adapts to the new conditions, however I'm pleased to say we had a really positive start to the day today with a good turn out of customers and everyone acting responsibly.
"What we didn't expect was an extremely heavy downpour of rain which resulted in Makinson Arcade, our Victorian Arcade being flooded in addition to some other areas of The Galleries.
"All members of the centre team were quickly on hand to clear up as quickly as possible and we are currently assessing the damage caused."
All but four shops in The Galleries were forced to close in March after the UK went into lockdown.
Those deemed essential and therefore allowed to continue trading were Heron Foods, Poundland, Home Bargains and Spectrum Community Health.
However, as lockdown restrictions were eased, non-essential shops across the country were allowed to open to the public from today.
