The force was called at 5.15pm yesterday (July 18) after a call described a fight in Market Square, involving a knife.
On arrival, they found a man lying in the blazing heat with what were believed to be stab wounds.
A Bedfordshire Police spokesman said: "We were called at 5.15pm yesterday (Monday) to reports of a fight in Market Square, Sandy, involving a knife.
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"Officers attended and discovered a man with what were believed to be stab wounds lying on the ground.
"The victim was taken to hospital and officers have launched a full investigation.
"Anyone with information is asked to contact police on 101 quoting the reference 40/41519/22, or alternatively contact Crimestoppers anonymously on 0800 555 111."