Residents at 17 care homes in Lincolnshire have been isolated after confirmed cases of coronavirus were found there.
Lincolnshire County Council said up to 30 had tested positive and were being kept away from other residents.
Professor Derek Ward, the authority's director of public health, said he expected the number of cases in care homes to increase in the coming weeks.
The authority monitors 270 homes across the county.
Infection prevention control measures were in place at affected homes including restricting the number of people going in and out of the properties, the council said.
According to the Local Democracy Reporting Service (LDRS), Newton House Care Home on Barrowby Road in Grantham is among those to have confirmed cases.
Barchester Healthcare, which runs the facility, said the home was still open despite there being two cases of coronavirus.
Two members of staff were also believed to be in self-isolation.
Professor Ward said carers had been given the "appropriate PPE (personal protective equipment)" to protect themselves, and the care and support of those who tested positive was "especially robust".
"We are doing everything we can to protect people and staff in care homes and we are keeping a close eye on what is happening in our homes," he said.
Public health officials were in regular contact with the care homes, he added.
One Lincoln care worker, who wanted to remain anonymous, said staff were "terrified" by the risks involved in caring for residents who may have coronavirus.
She said: "Our area manager has been advised as per government guidelines that we only need to worry about masks if clients are already showing symptoms, but it is already too late by then.
"The crisis facing the vulnerable will be catastrophic in the next few weeks and I'm on the verge of tears every day."