Four people killed as U.S. east coast shivers in temperatures as low as -50F

• Brother and sister die after falling through icy pond
• Woman found dead on driveway after slipping on ice
• Joint record for lowest-ever temperature in Maine as it plummets to -50F

At least four people died after an Arctic ice blast gripped large swathes of the eastern U.S. and sent temperatures plunging as low as a record -50F.

Brother and sister Joseph Cody, 12, and Grace Cody, nine, were killed when the ice pond they were sledding on gave way from underneath them in Southwest City, Missouri.

In North Haven, Connecticut, 50-year-old Denise O'Hara is feared to have slipped and knocked herself unconscious on the driveway of her home late at night - neighbours found her frozen body the following morning.

And in Lansford near Philadelphia Alan Kurtz, 49, died after sleeping in his car amid sub-zero temperatures.

Car trouble: A vehicle in New York City is entombed in ice after sub-zero temperatures swept across the east coast and caused chaos for motorists

Sub zero: Broken ice floats on the Delaware River in Camden, New Jersey. The northeast of the U.S. has been hit by record low temperatures

All four were victims of the coldest weather to grip America this winter so far.

It is being caused by an Arctic blast from Canada has swept down through the Mid West and spread across more than 20 states in the North and East Coast.

Temperatures were not expected to get above freezing anywhere affected but in Maine the wind chill could make it feel like -50F, a joint record.

So cold: Steam rises from houses in frozen Montpelier, Vt.

The coldest temperature ever seen in Maine is -50F which has happened twice: a remote site in northern Maine recorded a minus 50F reading on Jan 16, 2009, that tied a 1933 record set in Bloomfield, Vermont for the coldest temperature recorded in New England.

‘This is the coldest air we’ve had in about two years,’ said Michael Hill, a National Weather Service meteorologist in Caribou.

Fancy hat: A clothing seller expects to do a roaring trade in New York

Big chill: An ice skater in Montreal, Canada. Blasts of Arctic air have hit the north of the U.S., bring temperatures as low as minus 43C

Doctors warned that under such circumstances frostbite could set in in just 60 seconds. Even in warmer places such as New York, where temperatures could be -4F, the condition could begin in five minutes.

The deaths of Joseph and Grace Cody left the tiny farming community of Southwest City in shock with teachers describing them as ‘two of the brightest, most polite children they had dealt with’.

Frozen: A horse with a frost-covered face shivers in a field in Calais,, Vermont today

Such was the strength of feeling that residents carried out a candlelit vigil on Sunday night at the spot where they died Grace was in the ice and water for more than five hours before she was found, while her brother was pulled out after about an hour, said Southwest City Mayor Ryan McKee, a member of the volunteer fire department that responded to the scene.

Both died later in hospital.

‘Things like this just don't happen here,’ said William Goodwin, owner of Ozark Funeral Home in the town, which has a population of just 850.

Investigators in Philadelphia said it was unclear why Mr Kurtz spent the night in his car.

And in North Haven police were unable to explain how Miss O’Hara died, but it is thought that she may have perished from exposure to the freezing conditions.

The cold weather has led to teachers warning parents to make sure their children are bundled up on the school run so they don’t catch a cold.

Commuters were also braced for travel chaos amid treacherous conditions and ice on the roads.

New York’s Central Park was expected to hit high of 24F but wind chills made daytime temperatures feel more like 3F to 7F The National Weather Service predicted a high of 19F on Monday, the coldest it's been in New York City since Jan 16, 2009, when the high was 16F.

In the famous Bryant Park the fountains turned into giant blocks of ice whilst pictures of cars looked as if they had spent the night in a deep freezer.

In Pittsburgh, where the Pittsburgh Steelers took on the New York Jets in the NFL playoffs on Sunday evening, the temperature was about 13F at game time.

Fans told ABC News that they wrapped up in six pairs of trousers and three coats to stay warm.

Temperature not rising: A duck flies off at a frozen lake in Marlborough, Mass.