New coronavirus infections have more than doubled in a week in Birmingham, the latest figures show.
The city council has warned "we cannot afford to drop our guard" as the weekly number rose from 13.8 per 100,000 people to 28.1, with 321 new cases.
In neighbouring Sandwell - which was previously identified as an area of concern by Public Health England (PHE) - rates have dropped to below 20.
The rate is still significantly lower than the worst-hit areas.
In a joint statement on Friday with six other councils in the West Midlands - Coventry, Sandwell, Solihull, Dudley, Walsall and Wolverhampton - Birmingham City Council urged people and businesses to remain alert to the risks of coronavirus.
It also said, with thousands of university students expected to return to the region next month, social distancing would be fundamental to preventing campus outbreaks.
"People right across Birmingham and the wider West Midlands still have a huge part to play if we're going to avoid a further lockdown," council leader Ian Ward said.
"We can't afford to drop our guard now."
West Midlands Police has also issued a warning after reporting that officers had to shut down 125 parties in the area last weekend in a crackdown on illegal gatherings.
The local authority called for "continued vigilance to reduce the risk of a further significant spike".