Motorists may expect some delays when travelling through the intersection of St Hill Street and Ingestre Street after contractors accidentally cut through traffic loops.
The intersection traffic lights are currently operating on a set phase, a Whanganui District Council spokesperson said.
"Last weekend contractors working for a utility company inadvertently cut through the traffic loops in the intersection while digging a trench.
"The loops control the phasing of the traffic signals."
Whanganui District Council has set the signal phase manually, meaning they will operate for a set period of time before changing, even if there is no traffic travelling on the alternate phase.
The signal phasing repairs are unlikely to be completed until the end of next week.
"In the meantime, motorists and pedestrians must obey the traffic signals even if no other traffic is around."