20 million Americans face severe weather threat on East Coast

More than 20 million people on the East Coast are facing a severe weather threat Saturday.

The risk for severe thunderstorms stretches from New Jersey to South Carolina, up and down the I-95 corridor.

A severe thunderstorm watch has been issued for parts of Delaware, the District of Columbia, Maryland, North Carolina and Virginia until 6 p.m. ET, and expanded into parts of Pennsylvania and New Jersey until 9 p.m. ET.

A severe thunderstorm watch has also been issued for parts of South Carolina and North Carolina until 11 p.m. ET.

The main threats are damaging winds and large hail, but an isolated tornado is possible as well. Wind gusts could reach up to 70 mph in some areas.

The severe weather threat is part of a line of thunderstorms moving east with a potent cold front.

Elsewhere, heavy rain is expected in the Northeast Saturday night into Sunday, bringing a flash flood threat. Cities including Boston and Providence could be dealing with heavy rainfall into Sunday afternoon. Much of New England could see 1 to 3 inches of rainfall as this vigorous cold front sweeps across the East Coast.

In the South, there is also a risk for severe thunderstorms Saturday afternoon in south and central Texas, from Abilene to San Antonio. A severe thunderstorm watch has been issued for parts of central Texas until 11 p.m. ET.

More than 6 million people are under the threat for very large hail, with up to 3 inches in diameter possible. Wind gusts up to 70 mph and an isolated tornado are also possible.

ABC News' Kenton Gewecke contributed to this report.