A mysterious long black line pictured in the Kent sky has left both residents and experts puzzled.

The dark vertical apparition was pictured in Folkestone yesterday morning by a woman who “could not believe” what she was seeing.

The shadowy line was seen directly above Eurotunnel in Ashford Road and went up “as far as the eye could see”.

The skies were clear and the sun was shining at the time of the photograph. But, thunderstorms were forecast for later in the day.

The woman who pictured the phenomenon said: “I saw the line and took a photo to make sure it wasn’t my eyes deceiving me!

“I honestly have no idea what it could be. It was such a straight line so it obviously wasn't smoke from a crash or something like that.”

The Folkestone resident took a picture of the black line from her car near the roundabout along the A260 and told KentOnline she was surprised no one else had posted about it.

“The line went up as far as the eye could see. It went way past the clouds,” she said.

“I am hoping that someone else could shed some light on it. I can’t be the only one that saw it.”

Weather observer, Jeremy Procter, was also left baffled by the odd vertical line.

“It’s a very interesting photo,” he said.

“The line is definitely not any type of cloud. It is interesting that it appears to be partially obscured by a cloud in the middle and upper parts of the photo, indicating that it was not an optical fault,” he added.

Mr Procter has his own weather station at his home and formerly submitted a monthly weather report to the Sittingbourne Messenger.

He said: “Noticing the tall lighting tower on the right of of the picture, in certain light circumstances with the sun behind you can get a shadow effect.

“That’s the best possible explanation I can suggest!”

A spokesperson at Eurotunnel confirmed that the black line was not coming from their site.

In 2013, the Daily Mail reported on a similar black line pictured in Florida.

Mike Clay, chief meteorologist at the local station Bay News 9, was also left stumped by the unusual black line shooting down from a cloud.

The weatherman shared the pictures with some of his colleagues, one of whom came up with a possible explanation, suggesting that the dark line could be the shadow of a contrail.

Contrail is the condensation trail left behind jet aircraft. Contrails form when hot humid air from jet exhaust mixes with environmental air of low vapour pressure and low temperature.

For a contrail shadow to be seen, atmospheric conditions must be just right, with the sun hanging low on the horizon.