Bristol's Mayor says the city is at a "critical point" with cases almost doubling in the last seven days.
There has been a significant rise in the number of people in their twenties and late teens testing positive for coronavirus.
The latest available data shows 77% of positive tests for coronavirus in Bristol come from those under 30 years old.
In a press conference today (23 June), the mayor said he is "concerned" but added that he is confident people are playing their part to reduce transmission.
Bristol is now averaging 156 cases per 100,000 people and there are ten individuals in the city's hospitals who have tested positive for coronavirus.
He said: "We have gone above the national average before as well, and we came down.
"It is worth being aware of just how quickly these numbers can change.
"Our numbers went up incredibly quickly to over 500 and then they came down again very quickly as well, when we took the action that was needed.
"So, we know we can have an impact on the virus."
Speaking at a Bristol City Council cabinet meeting on Tuesday, he said: “We are at a critical point in the pandemic once again.
“The virus is circulating in our communities and putting additional pressure on our NHS.
“We are encouraging the city to get back to the basics – ‘hands, face, space’ – and if you’re going to meet people, wherever possible meet in fresh air where the virus struggles to transmit as effectively.
“Please make use of the testing facilities across the city for people with no symptoms of Covid-19, including rapid testing and our new walk-in site at Bristol Harbour.”
When asked whether there is a plan to roll out vaccines to those under 18, the Mayor said: "We have the capacity to do it because we have the vaccination system in place, with the vaccination centres.
"But obviously, a decision like that would be under health guidance. So, if that's what the guidance became, we have the facilities to do it, because that's what we've been doing.
"It would just be about opening the doors to those younger people, just like we've becoming down the age ranges over the last number of months anyway."