Hospital chiefs on Teesside said they are starting to see a second surge of coronavirus cases in their wards.
Twenty-five cases have been confirmed at Middlesbrough's James Cook University Hospital, with five people in critical care as of Tuesday.
It has separated one of its critical care areas for virus patients, as it did earlier in the year.
Adrian Clements, medical director at South Tees NHS trust, said: "The truth is Covid is coming back."
Councillors on Middlesbrough's health scrutiny panel were told the hospital had just seven or eight cases last week.
Mr Clements described control measures as "tight" but said rising cases in the community had led to staff catching the illness outside hospital and bringing it in.
He added: "Initially it was increased Covid numbers in the community, but we are certainly starting to see those numbers arrive in hospital.
"We will wait and see how bad the pandemic is and what the numbers look like, but we are now preparing for the potential worst-case scenario - and there's a duty for us to do that."
The number of coronavirus patients at James Cook University Hospital peaked at 150 during the first wave of the pandemic.
Bosses split the site in two in an effort to limit the spread of the virus and say they are looking at re-implementing the measure.
They are also making preparations for a Covid-19 assessment unit on site for people going into the hospital, the Local Democracy Reporting Service said.
Mark Adams, South Tees' joint director of public health, told the meeting there had been outbreaks on "three or four" wards.
The hospital had gone from seeing two or three cases per week to two or three each day, he said, and that he was "really concerned" about the virus being passed on to vulnerable groups.
On Teesside as a whole, figures published on Tuesday showed a total of 73 cases. Fifty-eight were recorded on Monday.