A 60-year-old woman is being questioned on suspicion of manslaughter after three people died at a care home.
Dorset Police said they received a report at 7.16am on Wednesday regarding three residents who were found dead at Gainsborough Care Home in Ulwell Road, Swanage.
Seven people were taken to hospital as a precaution and other residents from the address were evacuated to a location where they could receive appropriate care.
Police said on Wednesday the deaths are "currently being treated as unexplained", adding that detectives have confirmed "possible carbon monoxide poisoning is the primary line of inquiry".
Gas distribution company SGN - which said it owns and operates all of the pipes underground and up until the gas meter - said it completed safety checks and there has been no gas leak involving its network.
A spokesperson said on Wednesday: "Earlier this evening, we completed our safety checks at the Gainsborough Care Home in Swanage and can confirm there has been no gas leak involving our network.
"We'd like to assure the community that the mains gas network in their local area is sound. If anyone smells gas, they should call the National Gas Emergency Number on 0800 111 999."
Dorset Police said a 60-year-old local woman was arrested on suspicion of manslaughter on Wednesday evening and remains in police custody.
A police cordon remained outside the home on Thursday morning, with police tape on the hedges and officers standing outside.
Two Health and Safety Executive workers arrived at the scene on Thursday.
Janet White, 84, a retired magistrate who lives near the care home, said the incident was "devastating".
She said: "It is all very shocking and the fact that someone may be responsible in any way is difficult to comprehend.
"It's been very upsetting for people around here. The care home has links throughout the community.
"In my own case, my husband was cared for at home by Agincare and I have nothing but praise for them."
Gainsborough Care Home is run by Agincare and had been caring for 48 residents, all elderly and some with dementia.
"Something like this, when it happens where you live, is devastating for everyone," Ms White added.
George Manning, who has lived near the care home for several years, said: "We've never had any concerns about the place before.
"We were staggered when we saw what was happening yesterday with all the emergency vehicles, and then to hear someone had been arrested was shocking.
"I imagine it's going to be a big investigation before they get to the bottom of it."
Maggie O'Neill, who lives nearby, volunteered to help at All Saints Church in Swanage after discovering care home residents had been evacuated.
She said she later found out she knew one of the people taken to hospital following the incident.
"I knew someone that was taken to hospital, but I know nothing," she said.
"She's okay now, she has dementia. I think her family were able to go: they're very supportive."
The 76-year-old said she was one of the first people at All Saints Church, where the care home residents were taken.
"I was told by our dog walker people were being wheeled down so I quickly put my clothes on and went to help. I talked to the residents and served them tea.
"The atmosphere was tense.
"A few family members turned up, but there were a lot of volunteers, at least 20."Chris Moreton, 75, community response officer for Dorset Council, said the community has responded incredibly following the deaths.
Mr Moreton said the council has designated "rest centres" in place for when emergencies happen in the local area.
"We have a number of centres within Swanage that can respond to emergency events," he said.
He said All Saints Church is one of those centres.
Detective Chief Inspector Neil Third, of the major crime investigation team, said: "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."
Earlier on Wednesday, Dorset Police Chief Superintendent Heather Dixey told the press there was "nothing to indicate" danger to the wider community.
"The deaths are currently being treated as unexplained, and we are continuing to liaise with our partner agencies to establish the full circumstances of what has happened," she said.
"A significant multi-agency presence will remain in the area, including a police cordon, as we work with our partners to carry out an investigation.
"Following earlier inquiries, I can confirm that potential carbon monoxide poisoning is our primary line of inquiry, but I would stress that there is nothing to indicate that there is currently any risk to the wider public.
"Swanage is a very close-knit community and I know these very sad deaths will have significant impact on everyone here."