Officials are investigating a rise in coronavirus cases in Middlesbrough following a localised outbreak.
The 28 cases, connected to a small number of households in the Acklam, Linthorpe and town centre end of Marton Road area, were confirmed this week.
All those who tested positive are self-isolating and contact tracing is being carried out by health officers.
The town's infection rate remained relatively low compared to areas with local restrictions, the council said.
The council initially said there were 19 new cases but a further nine cases were confirmed on Friday.
Anyone known to have been in close contact with someone who has tested positive is advised to test themselves and to self-isolate until the results of those test have been confirmed.
'Taking strong action'
A testing centre at the disused Sainsbury's site close to the Riverside Stadium is open from 08:00 BST to 20:00, seven days a week, and has the capacity to test up to 800 people per day.
The council urged people to cover their face in public, wash hands regularly and keep a distance from others. Anyone with a high temperature, a new continuous cough or a loss or change to their sense of smell or taste should isolate and book a test.
Middlesbrough Mayor Andy Preston said: "We're taking strong action and alerting the public to protect people's health and jobs.
"Rest assured, we will do what's best for Middlesbrough."
South Tees Joint Director of Public Health Mark Adams said: "Although we have quickly established these cases are connected, they act as a reminder to everyone in Middlesbrough to take Covid-19 seriously.
"We have prepared for situations like this one and are reacting fast."
The local authority is also working with Public Health England's North East Health Protection Team.
They are also contacting anyone who used a taxi linked to someone who tested positive.
The taxi has not been used since 25 July. It was fitted with a protective screen when in use and the taxi company is providing details of any passengers who need to be contacted.