Armed police descended on Tesco Extra, at Battlefields, shortly after 4pm yesterday following a call out.
Officers set up a cordon moving people back away from the supermarket which closed during the four-hour 30 minute search.
West Mercia Police later scaled down the operation saying officers had carried out an extensive search.
But it is thought no-one was found.
The force did not comment on the nature of the investigation but said the alert had been made "in good faith".
Tesco reopened later that night and was open again from 10am on Sunday.
Images online showed armed officers scaling the roof of the store, clambering up staircases with battering rams.
A challenging search environment for the team this evening in Shrewsbury. It took a while but we had to be thorough. Sorry for the delays. Thanks for the assistance @4LeggedCops and @OPUShropshire @OPUWorcs @OPUHereford https://t.co/ZhjizfxyJe pic.twitter.com/LFev2jl9QI— Force Operations - West Mercia Police (@WMerciaForceOps) January 18, 2020
Officers from Hereford and Worcestershire along with dog handlers were called to help in the search, said force operations.
West Mercia Police called it a "challenging search environment for the team" as officers checked for any sign of a gunman.
Superintendent Jim Baker, from West Mercia Police, said officers on the ground were joined by the police helicopter and a fire and rescue service drone.
Following the initial call the force said in a statement: "Police received a report a man had been seen on the roof of Tesco Extra in Battlefield Road in Shrewsbury with what was believed to be a firearm."
Images showed buses parked up on Arlington Way as people were ordered to stay back behind the cordon.
The nearby Featherbed Pub and Carvery said it had lost about £2,000 in business in the evening through cancellations.
A member of staff who did not want to be named said around 100 bookings were cancelled, which included a 40th birthday party and a 60th birthday party.
The staff member said: "It’s dreadful I feel very sorry for the families who were looking forward to celebrating with us.”
Superintendent Baker added: "We take all reports involving firearms incredibly seriously and as such armed officers were deployed to the area and a cordon put in place.
"I’d like to thank members of the public as there was an increased police presence in the area with some disruption to local residents.
"The cordon has now been lifted however regular patrols will continue to be carried out in the area to offer reassurance to the local community.”
A Tesco spokesperson said: “We’re extremely grateful to the police in resolving this incident and pleased that nobody was hurt”
It is not known how many staff and customers were inside the store when the alert was made.