5PM UPDATE: Traffic around Northampton and Northamptonshire is building up after the closure of the M1 between junction 15 and junction 14.
Highways England is reporting severe delays on the A45 out of Northampton towards junction 15, with traffic at a standstill in parts.
The A43 southbound from Junction 15a towards Towcester is also experiencing severe delays. There are severe delays and stationary traffic on the A4 in both directions heading towards the A43 roundabout at Towcester, with further delays on the A43 northbound going towards the McDonald's roundabout in Towcester.
The M1 was shut by police after what a spokeswoman described as a "multi-vehicle" collision south of junction 15 for Northampton at 2.50pm.
The closed stretch, between junction 15 and for the A508 and junction 14 for the A509, is not likely to reopen until about 2am, according to Highways England.
A police spokeswoman said: "We would advise anyone heading that way to find an alternative route if possible."