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 taken initially to a church hall before being moved to “more suitable” accommodation.
Ten ambulances were called, along with a hazard response team and six fire crews.
Dorset Police launched an investigation, backed by the Health and Safety Executive, into the “unexplained” deaths.
The home had 48 residents, all elderly and some with dementia.
Fire crews and local people provided beds and blankets for the residents forced to leave the home.
Detective Chief Inspector Neil Third, of 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 one arrest to enable us to establish whether there have been actions or omissions which are grossly negligent and gather as much information as we can about what has happened.
“It is important to note that the arrest process also provides certain legal protection to individuals and I would ask for the media and public to avoid speculating any further now that legal proceedings are active.
“We know that the residents of Swanage will be feeling the impact of this incident immensely and we would like to thank everyone for the care and respect that has been shown throughout the day.
“Our local neighbourhood policing team will be on hand to provide support – we know this is a difficult time and we are doing all we can to minimise the impact on the community while we conduct inquiries in the area.”
A Dorset Council spokeswoman said the authority was working with other authorities to support the residents who had had to leave.
“Many of the residents are vulnerable people with significant care needs and, so, we are working with them to understand how to meet their needs in the short term and identify their next steps,” she said.