Cash payment machines for Auckland's Northern Gateway toll road have been hit by another technical glitch, which the Transport Agency has blamed this time on a telephone line fault.

An agency spokesman said yesterday both machines at the BP service centre south of the toll road were out of action from Thursday morning until TelstraClear cleared the fault at 3pm on Saturday.

The agency used electronic road-side messages to tell drivers the machines were not working and a "small number" of people who phoned the toll road's call centre were advised to pay their tolls electronically if possible.

Previous problems with the toll collection system were blamed on computer software failures which caused it to overcharge more than 20,000 motorists holding automatic payment accounts.