Snow and ice have swept across parts of the UK, with cold wintry conditions set to continue for days. AP / Reuters

Three boys aged eight, 10 and 11 have died and a fourth — aged six — was in critical condition after they fell into an ice-covered lake in Solihull, central England, on Sunday afternoon.

"Searches of the lake are continuing as we seek to establish exactly what happened and if anyone else fell into the water," West Midlands Police said.

"Three boys have tragically died after falling into the lake at Babbs Mill Park in Solihull yesterday afternoon," West Midlands Police said in a statement.

The boys suffered a cardiac arrest and 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," said police. "A fourth boy, aged six, remains in a critical condition in hospital."

Witnesses reported seeing other children on the lake, which froze during a cold snap that has hit swathes of Britain, but police have not reported anyone else missing.

Emergency services were quickly on the scene, with fire and police officers wading into the frozen water in their uniforms, Solihull Superintendent Richard Harris said in a news conference. One officer attempted to punch through the ice to get to the boys, he added.

Harris said the families were "absolutely devastated" and the fact it occurred during the Christmas period "adds to the tragedy." Identities of the victims will not be released until the families agree to do so, he added.

Arctic blast

The tragedy came as the UK was hit by heavy snow and freezing conditions, causing major travel disruption, on the eve of a national rail strike Tuesday that was already expected to bring the country to a grinding halt.

The UK has been experiencing a cold snap for several days, with temperatures dropping to -10˚C in some areas, although the Met Office said the temperatures were "not unusual for this time of year."

The service has issued yellow alerts for snow, fog and frost in several areas, including southeast and southwest England, and the north of Scotland. London Stansted airport warned of disruption.

"Our runway is temporarily closed whilst we undertake snow clearing," it said late Sunday, with many flights cancelled early Monday.

The airport later said that the runway was open and fully operational, but that travellers should still brace for delays. The airport is a main hub of budget airline Ryanair, which also cautioned about disruption to its flights at Gatwick, south of London.

"Due to ongoing severe snowy weather across the UK, runways at both Stansted and Gatwick have been temporarily closed tonight (11 December), disrupting all flights scheduled to depart Stansted/Gatwick during this temporary closure period," it said. Dozens of stranded passengers posted videos on social media showing snow-covered runways and planes stuck on the ground.

More than 50 flights were also cancelled on Sunday at Heathrow, the UK's largest airport, due to freezing fog.

Train and bus services in London were also severely affected after the dump of around four inches of snow overnight, which also forced the closure of parts of the M25 orbital road around the capital, the country's busiest motorway.

Some schools were also shut.

Agencies