Parts of the Northeast are under the threat of severe thunderstorms on Thursday, with 60 million people on alert for severe weather.

A severe thunderstorm watch is in effect up and down the I-95 corridor through 9 p.m. Thursday for cities including Richmond, Washington, D.C., Baltimore, Philadelphia and New York City.

Severe thunderstorm warnings have also been issued in some areas, including in southeastern Pennsylvania.

The main threat with these storms will be widespread damaging wind gusts to 75 mph. Hail and tornadoes are also possible.

A “large and extremely dangerous” tornado was located over Landenberg in southeastern Pennsylvania around 5 p.m. Thursday, the National Weather Service said.

In New York City, a teenager was struck by lightning in Central Park Thursday afternoon, police said. The teen is alert and conscious, police said.

The storms have led to power outages and flight cancellations along the East Coast.

More than 500,000 customers across the Mid-Atlantic were without power as of Thursday evening, primarily in Virginia, Pennsylvania and Maryland, according to PowerOutage.us.

Nearly 600 flights have been canceled nationwide on Thursday, according to FlightAware, with New York’s LaGuardia Airport the most impacted.

ABC News’ Melissa Griffin contributed to this report.