A burst water main will cause A1 Southbound between Langford and Stotfold and one lane Northbound to close until "early next week".
The teams will be working "24/7 throughout the weekend" to repair the main and the closures will be put in place later this afternoon.
An Anglian Water spokesperson said: “Due to a burst water main in the central reservation of the A1 in Biggleswade our teams will need to close both lanes of the road southbound between Langford and Stotfold and one lane northbound to ensure the safety of those who are working on the site.
"The closure will be put in place later this afternoon with a diversion in place and our teams will be working 24/7 throughout the weekend to have the repair completed.
“We expect to have the road reopened early next week. We would like to apologise for the inconvenience this will cause and thank everyone for their patience while we carry out this emergency repair.
"Please note the lane closures won’t be in place until later this afternoon."