Police are appealing for witnesses after the incident in High Street North, Dunstable.
They were called just before 5.30pm, to reports of a man with stab wounds. He was in the area between Union Street and Winfield Street.
Emergency services attended and the man, in his 20s, was taken to hospital where he remains in a critical condition.
Officers have launched Operation Buffalo, and are keen to speak to anyone who was in the area from 5.30pm onwards.
Detective Sergeant Ryan Barnes said: “We’re taking this incredibly seriously, and it’s important that we speak to anyone who was in the area at the time. If you saw anything out of the ordinary, we would like to speak to you. No piece of information is too small, and you could hold vital clues that will help us find out exactly what happened.
“I want to reassure our communities that we are investigating this thoroughly, and that it will continue to be a priority for us.”
An 18-year-old man has been arrested in connection with the incident and remains in police custody.
The incident happened as police were dealing with a stabbing incident off Cardigan Street in Luton. A man was airlifted to hospital
Anyone with any information is asked to call 101 quoting Operation Buffalo. Alternatively, report information online by visiting www.bedfordshire.police.uk/report or call independent charity Crimestoppers anonymously on 0800 555 111.