Pub customers are being urged to get tested for Covid-19 after 10 cases of coronavirus were confirmed at a bar.
Health officials said anyone who was at the Crown and Anchor in Stone, Staffordshire, between 16-18 July should get tested.
One person who tested positive after being at the pub also held a private gathering, causing a further spread, Staffordshire County Council said.
In a post shared on Facebook, the pub said it would close.
Dr Richard Harling, director of public health at the council, said: "This appears to largely be a young adult demographic, young adults in the 18-21 age bracket."
Dr Harling said there was a tracking system in place at the Crown and Anchor, "but it didn't capture the number of patrons very comprehensively".
The council has encouraged anyone who may have been in close contact with someone at the pub that weekend and people who may have been drinking in Stone then and are currently experiencing symptoms to get tested.
Ayrron Robinson, who filmed the pub, said he was "angry" and "frustrated" at seeing the crowds.
"We're talking a hundred, two hundred people in there," he claimed.
"You can hear them. I've got double glazed windows, [but] you can hear them."
A walk-in test centre was open at Crown Street car park in Stone and more than 300 people were tested in the first two hours, with queues forming.
For the next four days a mobile testing unit will operate by appointment only instead. It will be open from 11:00 to 15:00 BST on Thursday and Friday and from 10:30 to 15:30 on Saturday and Sunday.
People who are not experiencing symptoms will need to choose the "I am in a lockdown area with a coronavirus outbreak" option, even though there is no lockdown in Stone.
We are experiencing a high volume of visitors already, so just a reminder that you have until 5pm to come and get tested. Please stagger your visits throughout the day to help minimise delays at the site.— Staffordshire County Council (@StaffordshireCC) July 29, 2020
Thank you for your patience. https://t.co/TBycQx7VWP
After images of the pub were posted online, local MP Sir Bill Cash said: "It shows a degree of lack of concern for other people and it just is completely unacceptable and inappropriate for people to gather in such circumstances."
Stafford Borough Council said it would cancel the Stone Farmers' Market which was due to take place this weekend.
Another pub in the town, The Swan, said in a statement on Facebook it would stay closed in light of Covid-19 cases in the area.
Owner of Stonebaked Cafe Deb Wilkinson said: "Something like this sets people back.
"People will be scared to come out again really, especially in a little town like this."
Councillor Ian Parry said: "What we've seen is partly some selfish behaviour that's going on and we need to remind ourselves that we are responsible to each other during this crisis."
He said the town was busy on Wednesday and claimed "it's very safe to come to Stone".
The BBC has approached the Crown and Anchor for comment.