Detectives investigating the deaths of three people at a care home in Swanage, Dorset, have arrested a 60-year-old woman on suspicion of manslaughter.
Seven people were taken to hospital after the alarm was raised early on Wednesday morning.
The Gainsborough care home was evacuated and other residents were initially taken to a church hall before being moved to “more suitable” accommodation.
Ten ambulances were called along with an emergency team and six fire crews.
Dorset Police launched an investigation, supported by the Health and Safety Executive, into the “unexplained” deaths.
The home had 48 residents, all elderly and some with dementia.
Firefighters and local residents provided beds and blankets for the residents who were forced to leave their homes.
Detective Inspector Neil Third, from the Major Crime Investigation Team, said: “Our heartfelt thoughts and condolences are with the families and loved ones of those who tragically died and they are being supported by officers.
“As part of our investigation we have made an arrest to enable us to establish whether there have been acts or omissions which are grossly negligent and gather as much information as we can about what is happened.
“It is important to note that the arrest process also provides some legal protection to individuals and I would ask the media and the public to refrain from further speculation now that legal proceedings are active.
“We know the residents of Swanage will feel the impact of this incident hugely and we would like to thank everyone for the care and respect shown throughout the day.
“Our local police team will be on hand to provide support – we know this is a difficult time and we are doing everything we can to minimize the impact on the community while we carry out inquiries in the area.”
A spokesman for Dorset Council said the authority was working with other authorities to support those residents who had to leave.
“Many of the residents are vulnerable people with significant care needs, so we work with them to understand how they can meet their needs in the short term and identify their next steps,” she said.