CHICAGO: A massive Christmas storm that whipped up tornadoes, ice and snow from the Gulf of Mexico to the Great Lakes has killed at least seven people and grounded more than 2,000 US flights.

The storm snarled holiday travel as people were warned to stay home rather than brave the strong winds, freezing temperatures and treacherous roads.

The National Weather Service warned of “dangerous travel conditions due to snow and ice covered roads” and said the weight of ice and snow could knock down power lines and trees.

Already, more than 200,000 people were without power, with tens of thousands of holiday travelers stranded across the country.

The weather service forecast up to 18 inches of snow from New York state up to Maine and warned of freezing rain, tornadoes and severe thunderstorms all the way down to the Carolinas.

Albion, Illinois had already recorded 18.3 inches of snow by Wednesday afternoon while parts of Pennsylvania had recorded as much as half an inch of freezing rain as the storm continued to pound the region.

The Indiana state police said it had responded to 159 crashes near Indianapolis in just the first few hours of the storm.

More than 1,500 US flights had been canceled by Wednesday evening, after 536 were grounded on Tuesday, according to flight tracker FlightAware. Another 276 were already called off for Thursday.

Scores of homes and businesses were damaged on Tuesday after 34 tornadoes were reported in the southern US states of Texas, Louisiana, Alabama and Mississippi. The governors of both Mississippi and Alabama have declared states of emergency.

More than 200,000 people remained in the cold and dark on Wednesday after the storm knocked down power lines in Arkansas, Mississippi and Texas.

The regional utility company said it was bringing in outside crews to help, but it could be a week before service was fully restored.

Two children were killed after their mother lost control of her vehicle on an icy road in Arkansas on Christmas Day, the state police said. Another person was killed in the state early Wednesday as a result of the storm.

A dozen people were hurt in a 21-vehicle pileup caused by icy roads in Oklahoma City that started when a truck jack-knifed on a major interstate and oncoming cars were not able to stop on the icy roadway, the Oklahoman reported.

Two women were killed in separate crashes in the state on Christmas Day, the state highway patrol said.

A man was killed in rural Louisiana when a tree hit his home on Christmas Day, and a Texas man died in similar circumstances in a Houston suburb, local media reported.