Train passengers are once again being hit with a spate of train cancellations and bus replacements as mechanical problems continue to plague the fleet.

Services to Porirua, Taita and Melling are so far affected.

The problems come after days of mechanical problems hit the trains last week because of strain put on the fleet by the cold weather.

Tranz Metro Manager Scott Brooks said staff were still trying to fix all the problems, and was working as quickly as it could.

Six trains in the depot can not run because of a "combination of mechanical failures - particularly brakes, traction motor and pantograph issues".

A further 13 trains have "operational restrictions" due to mechanical problems.

"We are using all of the available Matangi to assist with peak services and will continue to work through these issues as quickly as we can."

Most of the affected trains are Ganz Mavags.

On Thursday eight services were cancelled, and a further 10 were cancelled on Friday - about 2.5 per cent of services.

About 2 per cent of services have been affected today.