Three boys aged eight, 10 and 11 have died after falling through an icy lake in Solihull, police have confirmed.
A fourth boy, aged six, remains in a critical condition after the incident at Babbs Mill Park on Sunday afternoon.
A search is continuing after unconfirmed reports up to six children may have fallen in, but authorities warned it is "no longer a search and rescue operation".
The four children were all in cardiac arrest when rescue teams pulled them out.
They were taken to hospital but police said three of them "could not be revived".
Reports from the scene and social media videos indicate they were playing on the ice and fell through, the fire service said.
Search teams were still using boats and wading in the lake on Monday - and police said they would continue until they are "100% certain" there are no other victims.
One of the first officers on the scene entered the lake in his uniform and tried to punch through the ice to help the boys, said Superintendent Richard Harris from West Midlands Police.
Members of the public also jumped in.
Firefighters and specialist water teams arrived at the lake and managed to pull the boys out. They were given CPR and taken to hospital but all four arrived in a critical condition.
Police said it's currently unclear how long they were in the freezing water.
One witness told Sky News he'd seen firefighters smashing the ice and a number of people in distress.
The children's names haven't yet been released and police said they were supporting their "absolutely devastated" families.
The boys' schoolmates are also getting support.
Teams in boats used torches to continue searching the lake overnight.
One police officer involved in the initial search suffered mild hypothermia and was taken to hospital but has now been discharged.
Superintendent Harris said at Monday lunchtime that they were still trying to piece together exactly what happened but that no one had contacted them to report anyone else missing.
But because of conflicting reports about how many children were on the lake, the search will continue until police are certain no else went in.
Local MP Saqib Bhatti visited the scene on Monday and praised emergency services for their "heroic" efforts.
"The (search) operation went on all night in these really tough conditions," he said, adding that "the whole community will be feeling the pain of this".
Police have asked people not to speculate or share any video of the incident.
Richard Stanton, area commander for West Midlands Fire Service, urged parents and carers to remind their children about the dangers of frozen water.
He said: "Please, adults and children alike, stay away from open water. Under no circumstances venture on to ice, regardless how thick or safe you think this ice may be."