Buses in Bishop Auckland are being targeted by vandals who pelt them with rocks.
Durham Police said they were investigating several incidents that have taken place since mid-August.
The most recent happened in the South Church area last week, near to St Andrew's Church.
They said the culprits create a blockade in the centre of the road causing the bus to slow or stop. Rocks or stones were then hurled at the bus.
Police are appealing for witnesses.