A teenage photographer's shots of The Beatles' first US concerts are expected to sell for £250,000 at auction.

Mike Mitchell, just 18 at the time, snapped hundreds of never before seen photographs of the band's performances at the Washington Coliseum and the Baltimore Civic Centre in 1964.

He also attended a press conference ahead of the Washington performance - their first in the US - and the band's arrival at Union Station.

One shot, taken from behind, shows the back of each of the fab four's heads other than John Lennon who is turned to the side talking to his bandmates.

The negatives, taken only with ambient light since Mitchell had no flash, sat for decades in his basement until they were fully realised as luminous records with the emergence of digital technology.

The complete archive is made up of more than 400 negatives from the two concerts - 46 of which were seen for the first time in 2011 when they were digitally restored as high quality prints and sold at a Christie's auction in New York for an accumulated 362,000 US dollars (£224,000).

The entire collection - including the negatives and copyright of the those sold in New York - are to be unveiled and sold at a Beatles auction in Merseyside later this month.

Apart from the 46 images used in 2011, the remainder have never been seen.

Auctioneer Paul Fairweather labelled the collection an "incredible archive".

He added: "The unique combination of perspective and light sets them apart from any other Beatles photographs of that period.

"This was reflected in prices achieved for a small selection of prints in 2011, so for the entire archive to be sold with copyright, this is a unique opportunity for collectors and investors alike."

The photos will go under the hammer as part of Omega Auctions' Beatles Auction on March 24.