Covid cases in Blackburn with Darwen - which has the highest number of infections in England - have peaked, Public Health England figures suggest.
Driven by the Delta variant, Blackburn with Darwen currently tops the list for cases after overtaking Bolton in May.
Council leaders said rises in the rates of cases were already slowing, thanks to surge testing and vaccinations.
They said the government's four-week delay in lifting restrictions allows an opportunity to drive down infections.
Boris Johnson said Covid measures must remain in place until 19 July because of the rapid spread of the Delta variant.
Data shows 897 cases were recorded in Blackburn with Darwen in the seven days up to 10 June - the equivalent of 599 cases per 100,000 people.
Although it is up week on week from 548.4, it is below the figure of 667 recorded for the seven days up to 7 June, the highest for the area since mid-January.
In a joint statement, the leader of the authority Mohammed Khan, adult services director Sayyed Osman and director of public health Prof Dominic Harrison they were "optimistic" rates will drop, reported the Local Democracy Reporting Service.
"This delay presents Blackburn with Darwen with an opportunity," they said.
The trio said surge testing and extra vaccinations for over-18s in the past month were having an impact.
"Although we have seen increases in positive Covid cases, our rate of increase is now slowing, and we expect to see this improve until our case rates eventually plateau, and then begin to decline," they said.
"We need to make the most of this opportunity."
They urged residents to "pull together and do everything they can to help get control of our virus rates" - including having a vaccine if eligible.
Bolton currently has 308.8 cases per 100,000 of population, down from a peak of 452.8 in mid-May.