Cross Street was closed off as firefighters were called out to Co-op Travel at about 10.50am, but on arrival, there was no fire – just smoke.
Robin Evans, incident commander for Shropshire Fire and Rescue, said: "The incident started out in Co-op Travel, caused by a toaster that was left unattended.
"Both Co-op Travel and Designs In Mind were heavily smoke logged as a result.
"We've now removed the source and cleared the area of smoke."
Mr Evans urged the public to "be vigilant" around cooking.
He added: "I want to remind people that cooking shouldn't be left unattended, please remain vigilant when cooking."