Witnesses to the Solihull lake tragedy reportedly shouted "it's not safe" moments before a group of children plunged into the water to their deaths.
Three boys - aged eight, 10 and 11 - died after being pulled from the water, while a further two youngsters are missing and feared dead.
It is thought they had been playing on the ice as the horrific incident unfolded.
Emergency services were called to reports that six children had fallen into the lake, and crew members plunged into the icy water in a desperate rescue effort.
One police officer was treated for hypothermia, it was confirmed.
Specialists scoured the water overnight for the missing children, but officials said that because of freezing temperatures, there is little chance of survival.
The four children were pulled from the water were last night on life support after suffering cardiac arrests during the tragedy.
Three have since died, police confirmed this morning.
Witnesses said emergency crews were seen "smashing through" the ice on the lake's service.
One, a 23-year-old identified as Sophie, told the Daily Mail : "There were a group of youngsters playing near the lake which was completely iced over.
'Two of them had gone onto the lake and people were shouting at them that it wasn't safe.
"Then the ice cracked and the leg of one of the boys went in."
Sophie, who said she knows a member of one of the boys' family, said three more people went in to help. She said she saw four children being taken onto an ambulance.
Flowers were today seen being left at the scene, Birmimgham Live reports.
A huge 999 operation was launched after police, ambulance and fire crews were called to the scene, Birmingham Live reports.
Confirming the devastating news, a West Midlands Police spokesperson said this morning: "Three boys have tragically died after falling into the lake at Babbs Mill Park in Solihull yesterday afternoon.
"The boys, aged 12, 11 and 8 were rushed to hospital after being pulled from the water.
"Sadly, they could not be revived and our thoughts are with their family and friends at this deeply devastating time. We’ll have specialist officers offering them as much support as we can.
"A fourth boy, aged 6, remains in a critical condition in hospital."
Specialist teams spent the night scouring the lakes after authorities said it would "no longer be a search and rescue operation" as temperatures plummeted.
This morning's police statement continued: "Searches of the lake are continuing as we seek to establish exactly what happened and if anyone else fell into the water.
"We understand how distressing this is for the families and the wider community.
"We would ask people to not speculate or share any video footage at this stage."
One police officer was being treated for hypothermia after going into the water to rescue the children, a press conference was told last night.
Police have not confirmed if the children were siblings or their gender at this stage.
A school near the huge Babbs Mill Lake search operation was closed today - with a plea for people to keep those affected "in their prayers". St Anthony's Primary School at Kingshurst tweeted last night that it would be shut today.
Miss Nicola Crehan, principal of CTC Kingshurst Academy, the local secondary school, said: "The community at Tudor Grange Academy Kingshurst has been deeply saddened by the incident that occurred at Babbs Mill Lake yesterday.
"We are not aware of any direct links with students at Tudor Grange Kingshurst Academy, but we will continue to support the wider community throughout this period of loss and beyond.
"We are proud to be part of this tight-knit community and we offer our thoughts and support to all those that have been affected.
"This morning we spoke to all pupils about the incident. We have on standby, a fantastic and experienced safeguarding team who will work hard in supporting any children or families that require additional care.
"We stand by our community on this sad day."
Today the leader of Solihull Council broke down in tears as he visited the scene. Councillor Ian Courts said: "This is just about as bad as it can get. This is a dreadful situation.
"We are completely stunned by what's happened. We are still awaiting more news.
"Our thoughts and prayers have to be with the families in this situation. It's terrible, I can hardly imagine what the families are going through at this time."
West Midlands Ambulance Service tactical commander Cameron McVittie told reporters that the four children were in cardiac arrest when they came out of the water, and are currently on life support.
He said: "There's no clinical updates at this stage, as stated they were all in a critical condition on arrival at hospital."
He added: "Unfortunately, the children in the water were in cardiac arrest and were receiving advanced life support en route to hospital."
He said two were taken to Birmingham Children's Hospital and two to Heartlands in Birmingham.
Richard Stanton, West Midlands Fire and Rescue Service area commander, said: "When the fire service arrived at the scene, we were made aware there were up to six people in the water.
"So after rescuing the four children, we have continued the search and rescue operation to confirm whether there were any more in the water."