The A47 has been shut at Guyhirn as emergency services try and locate a man in the river.
Officers were called to the scene at 12.15pm due to concerns for a man.
The road was shut between Guyhirn and Rings End at 12.50pm.
Emergency services remain at the scene trying to locate the man.
A minor collision has been reported in the traffic queue that has built up, and traffic is described as being very heavy on the A47 and A141 around the incident. Motorists are advised to avoid the area if possible.