Up to 15 people are feared dead after a suspected gas explosion saw a block of flats collapse - with temperatures plummeting overnight.
The emergency services are now treating the scene in St Helier, Jersey, as a "recovery operation" rather than search and rescue, police have confirmed.
Teams have worked through the night, with three people so far confirmed dead and a dozen more missing following the blast at around 4am yesterday.
Temperatures dropped to around 4C on the Channel Islands in the early hours of Sunday as an Arctic weather front continues to blanket the UK, bringing a fierce cold snap.
The Jersey flag will fly at half mast on official buildings "as a sign of respect" from 8am tomorrow until sunset on December 23, while an island-wide minute's silence will also be observed on Monday, the government said.
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Fire chief Paul Brown has today reassured islanders they can have "confidence" in their emergency services despite crews being sent out nine hours before the incident to reports of gas.
Jersey Police Chief Officer Robin Smith also said this morning: "It is with sadness that I am confirming that the search-and-rescue operation had been moved to a recovery operation.
"The decision was made after a detailed assessment and following the use of specialist K9 units.
"Disaster victim identification (DVI) strategies are in place and specialist officers are surveying the scene with fire and ambulance services and tactical advisers from urban search and rescue (USAR)."
He said yesterday that it was a "protracted incident" that could "go on for days, maybe weeks", as he warned that people should be prepared for the possibility of "more fatalities".
He added: "It is a scene of utter devastation. It has completely collapsed. The number one priority is working out if there's anyone alive in that debris."
Firefighters and specialist rescue teams, including a dog, were pictured at the scene on Saturday night.
The footage captured some of the devastation and debris behind the cordon - including piles of rubble, crushed cars and a blown out window in the neighbouring building.
The government said: "We're on site coordinating a methodical and meticulous multi-agency search effort.
"This involves a number of stages, including vacating the site for short periods to allow dogs to enter, and the careful movement of debris."
Jersey Fire and Rescue Service's chief fire officer, Paul Brown, said yesterday: "I can confirm the fire and rescue service did attend at 20.36 yesterday evening... I know that they did conduct an investigation but at the moment what I'm focused on is the emergency response."
In today's briefing, when pressed the potential failing, he said: "It is a tragic tragic situation. We are all devastated that islanders have been lost and that families and loved ones are suffering today.
"It's awful but islanders can have confidence in their emergency services. Islanders can have confidence in the States of Jersey Fire and Rescue Service.
"I think that what those families deserve and what those families will absolutely receive is openness and transparency," he added.
Mr Brown declined to answer whether anyone had been suspended or put on immediate leave.
Asked at the briefing if any criminal investigation had been launched or would likely be, Mr Smith said: "We rule nothing in and nothing out."
The cause of the fire has not yet been confirmed, but Mr Smith said it "looks likely" that it was caused by gas.
"It seems likely but we don't know," he said.
Asked if police would be holding anyone accountable, he said: "We provide the facts."
Chief Minister Kristina Moore said at least three people had died, describing the incident as an "unimaginable tragedy" for the Channel Island.
Meanwhile, Mr Smith said that around 12 people were missing, adding: "My hope, of course, is that the number is a lot less."
The police chief said it was a "protracted incident" that could "go on for days, maybe weeks".
He described said the scene in St Helier as one of "tragedy" and "complete devastation".
Andium Homes, a state-owned but independent company which rents out thousands of properties on the island, said it is focusing on supporting residents at the estate.
Gas supplier Island Energy said it was working with the fire service to "understand exactly what has happened".
Residents of the flats have been moved to St Helier Town Hall, where they are being supported.
A candlelit vigil was held for those affected by the tragedy at the nearby Parish Church of St Helier on Saturday night, and a note had been left on a noticeboard reading "give strength to those families who've been lost this week".
Associate Rector James Porter said the incident had had a "profound" impact on the community, particularly because it came days after three fishermen went missing at sea off the west coast of Jersey.
Speaking at the church, Mr Porter, 48, told the PA news agency: "The church here is right in the heart of the town and just a few hundred metres down from where the tragedy happened.
"This has affected the community in a profound way.
"It's a very small community in Jersey, and lots of people know lots of people, so there are lots of links.
"I think following on from the tragedy with the lost fishermen earlier in the week as well, it's been hard for people to digest."
L'Ecume II - an 18-metre wooden fishing vessel - sank five miles west of Jersey after colliding with the freight ship Commodore Goodwill at around 5.30am on Thursday.
Searches for the three men on board, including the captain who has been named in reports as Michael "Mick" Michieli, were called off at sunset on Friday.
