Parts of Essex have recorded the highest weekly coronavirus case rates since the pandemic began.
In the week leading up to 21 December, Brentwood, Epping Forest and Thurrock all had rates of more than 1,350 cases per 100,000 people.
The previous highest weekly rate recorded was in Nottingham in October.
A spokesman for Essex County Council said increased testing on top of an already high infection rate meant the figures "are not a surprise".
Brentwood's rate of 1,419 cases per 100,000 people in the week up to 21 December is now the highest recorded across England since the start of the pandemic.
The figures from the government's coronavirus database show there were 1,376 cases in Epping Forest and 1,361 cases in Thurrock per 100,000 people during the same week.
There was 1,336 cases per 100,000 people in Nottingham in the week leading up to 8 October.
"Essex's infection rates per 100,000 population were already among some of the highest being recorded," the council spokesman said.
"We have recently increased our testing capacity particularly in the south of the county where rates have been high and as this will have identified more cases, the figures are not a surprise."
The spokesman said the county's public health teams had been "focussed in recent weeks on testing people without symptoms, and has opened three lateral flow device testing centres, with several more due to open in the next two weeks".
He said encouraging people to get tested "is a central part of our strategy to break the chain of transmission, but inevitably means that more positive cases will be identified".
The whole of the county was moved into tier four restrictions on 24 December.
What are the restrictions in tier four?
- Residents should stay at home, unless they have a "reasonable excuse" such as work or education
- All non-essential shops must close
- Hairdressers and nail bars must close
- Indoor entertainment venues must close
- Gyms and indoor swimming pools, indoor sports courts and dance studios must close
- You cannot meet other people indoors, unless you live with them or they are part of your support bubble
- People should not leave tier four areas or travel abroad, except for limited reasons (including work and education)
- Weddings and civil partnership ceremonies are only allowed in exceptional circumstances