A campaign to buy and exhibit JMW Turner’s earliest known oil painting in a museum has raised more than £100,000 in five days.

Bristol City Council, which owns Bristol Museum and Art Gallery, wants to buy The Rising Squall, which depicts the Avon Gorge before Clifton Suspension Bridge was built.

Although the £100,000 target has been reached, the authority has said extra money will strengthen its bid when the piece is sold at Sotheby’s auction house on Wednesday. It is estimated to fetch between £200,000 and £300,000.

The council’s head of culture and creative industries Phillip Walker said the authority had been “humbled” by people’s “generosity and support”.

The piece was painted in 1972, when Turner was 17, and is the first oil painting ever exhibited by Turner. It is believed to be his only artwork depicting Bristol.

Turner’s signature was only discovered on the piece last year when the canvas was cleaned during a restoration project.

Prior to that, it has been missing for 150 years.

Kate Newnham, senior curator of visual arts at the museum, said: “It’s overwhelming to have received such an incredible and positive response from the people of Bristol and beyond.

“It just goes to show the importance of access to art and culture to everyone.”