Aliens, freak weather storms and archaeological remains have all been blamed for the mysterious phenomena of crop circles.

But police hope they will crack at least one case after a crew from the Suffolk branch of the National Police Air Service saw a “circle” in a field near Witham.

The crew, who were returning to their Wattisham base after a call out regarding a concern for welfare on Monday, took to Twitter to say “All in order but did see some interesting crop circles!”

Although some crop circles, or crop formations, consist of complex shapes and up to 2,000 different elements, a spokeswoman for Suffolk police said the design spotted by the helicopter crew in Essex was made up of a single offensive shape.

The sighting was passed on to officers on the ground who then investigated the circle.

A spokeswoman for Essex Police said: “The police helicopter was flying over Witham on Monday, July 7 shortly before 9.30pm and observed a group of youths on Allectus Way, surrounding a crop circle.

“Police on the ground spoke to the youths.”

She added: “No criminal offences were observed. Enquiries continue.”

The incident is not the first case of crop circles in the region with reports in both Suffolk and Essex, mostly near roads and residential areas.

At the peak of the crop-circle phenomena during the late 1990s and early 2000s, five huge crop circles appeared in a field of wheat close to the Copdock Mill interchange, with the largest circle measuring 35 metres across.

Anyone with information about the circles near Witham should contact Essex Police on 101.