Heavy thunderstorms and high winds hit the north-east US on Thursday, felling trees and power lines and causing a state of emergency to be declared in the upstate New York city of Elmira.

Two people were killed in the storms: a 61-year-old man who died after scaffolding collapsed outside a church in Brooklyn, and a woman who was hit by a tree in Pennsylvania.

Some 33,000 people were left without power following the storms, which moved through New York, New Jersey, Pennsylvania and Connecticut.

Some of the most extreme weather came in Elmira, where winds felled trees and damaged cars and buildings. The storm struck the city at around 4pm on Thursday, CBS reported.

Elmira declared a state of emergency, and a shelter was opened for displaced residents. Pictures showed damage to trees and powerlines, while the roof was blown off an old warehouse.

A woman who was camping in Genesee, Pennsylvania, was killed when she took refuge from the storm in her car and a tree then fell on it, according to John Hetrick, director of emergency services for Potter County.

In Brooklyn, a 61-year-old man in the Cobble Hill neighborhood died when scaffolding at a church collapsed on him as the storm passed through at around 8pm, police said.

"It's possible that lightning struck the top of the roof, causing some bricks to fall on top of the scaffolding, causing the scaffolding to fall on top of the victim," said a spokesman.

Reuters reported that "more than 100,000" people were without power following the storm. Pennsylvania residents accounted for the majority of those without power, with more than 85,000 customers in the dark early Friday, while roughly 34,000 people in New York were without power and some 13,500 customers in eastern Ohio were still offline, according to AEP Ohio.

"The Line Storm," a painting by John Steuart Curry, which may have been inspired by a derecho in Kansas

There was much discussion on Thursday as to whether the storm would develop into a derecho. In hindsight on Friday, no one quite seems sure whether the storm attained that status. But for those who might not have heard of a derecho, the National Weather service explains the phenomenon: