The severe thunderstorms that blasted the region midday Wednesday killed at least three people and knocked out power to tens of thousands, officials said.

And threatening weather reappeared Wednesday night, as the National Weather Service announced a tornado warning for parts of Philadelphia, Burlington, Camden, Delaware, Gloucester, and Montgomery Counties.

As of 8:30 p.m., the weather service had not received any confirmed reports that a tornado touched down in the Philadelphia region, but the skies over the city appeared ominous.

Wind gusts of 60 mph were measured at Philadelphia International Airport, the weather service said.

The storm earlier Wednesday — classified as a derecho, based on the speed of the wind and swath of damage — caused two deaths in Lower Merion Township, and one in Lower Moreland Township, according to Montgomery County officials. They said that as of 5 p.m., nearly 140,000 people remained without power.

In Delaware County, officials said a fatal house fire broke out during the height of the storm, killing a man trapped inside.

The official cause of the fire in Nether Providence Township was under investigation Wednesday, according to Police Chief Dave Splain. He declined to link the storm to the blaze, but did say neighbors reported hearing the sound of a nearby electrical transformer “surging” and then losing power moments before the fire was reported.

The weather service defines a derecho as a long-lasting thunderstorm with wind damage extending more than 240 miles and gusts of at least 58 mph along most of the storm’s path.

“They’re relatively rare,” said Robert Deal, lead forecaster for the weather service in Mount Holly. The last one was recorded in the Philadelphia region in 2012.

The storm started around 7 a.m. near Lake Erie, Deal said, before sweeping across Pennsylvania. Wind gusts reached 83 mph in Berks County, and spanned 59 to 76 mph in Philadelphia and its surrounding counties, according to the weather service.

Speeds of 59 to 67 mph were recorded in Burlington and Camden Counties. By the time the storm reached the New Jersey coastline, around 2 p.m., wind gusts had hit 89 mph in Brick Township, Deal said.

“Any time you’re getting measured wind gusts of 80 mph, that’s exceedingly rare for anywhere in the country,” Deal said.

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The weather service doesn’t have any indication a tornado took place during the day, Deal said. But when speeds are strong enough, “it doesn’t matter whether the winds are spinning or going straight."

Staff writers Oona Goodin-Smith and Vinny Vella contributed to this article.