CHICAGO  - A massive winter storm system that whipped up tornadoes, ice and snow from the Gulf of Mexico to the Great Lakes and killed at least six people on Christmas was moving slowly eastward Wednesday.

Hundreds of flights were cancelled and 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.

It forecast up to 18 inches of snow (46 centimeters) from New York state up to Maine and warned of freezing rain and tornadoes all the way down to the Carolinas. Areas in the Rocky Mountains could also expect about a foot (30 centimeters) of snow on Wednesday. Nearly 700 US flights had been cancelled by Wednesday morning after more than 500 were cancelled on Tuesday, according to FlightAware.

"We expect the number of cancellations and delays to rise today and tonight as the storm hits the New York City area this afternoon and continues with high intensity through the evening," FlightAware chief Daniel Baker said. "The biggest factor on both coasts is high winds and winds not aligned with runways."

The major hub of Dallas-Fort Worth had halted all flights until 11 am Wednesday after having cancelled nearly 400 flights on Tuesday due to the strong winds, snow and ice.

Scores of homes and businesses were damaged Tuesday after 34 tornadoes were reported in Texas, Louisiana, Alabama and Mississippi.

A 25-year-old man was killed in a Houston suburb after a tree fell on his pickup truck Tuesday, the Houston Chronicle reported. A dozen people were hurt in a 21-vehicle pileup caused by icy roads in Oklahoma City that started when a truck jackknifed on a major interstate and oncoming cars weren't able to stop on the icy roadway, the Oklahoman reported.

Amanda Sue Goodman, 28, was killed in a separate crash in rural Oklahoma after the driver of the vehicle she was riding in lost control and hit a big rig on the snow-covered highway. The driver and a 4-year-old girl were also hurt.

Allen Sullivan, 53, was killed when a tree hit his home in rural Louisiana on Christmas Day, the News Star reported.