The latest batch of KiwiRail's new DL class diesel electric locomotives has arrived at the Port of Tauranga.

The 15 engines, ordered in 2016, are joining the 48 the national rail operator already has on its books, bringing the total number in the class to 63. The first DLs arrived from Chinese manufacturer CRRC's Dalian Locomotive Works in 2010.

After unpacking and initial testing at the Mount Maunganui KiwiRail yards, the locomotives will be transferred to Hamilton to be commissioned. They're expected to see service on all main lines in the North Island, including the East Coast line through Tauranga, and the North Island Main Trunk.

The move to add a further 15 locomotives to the DL fleet was made by KiwiRail following its controversial decision to mothball the Main Trunk electrification, which is still expected to go ahead despite opposition from environmental groups and unions.

KiwiRail also raised eyebrows in deciding to stick with the Chinese manufacturer after earlier units of the class suffered from unreliability and asbestos contamination issues.

Last year the incoming Labour-led Government pledged to direct KiwiRail to reverse the decision to discontinue using electric locomotives on the Main Trunk, and has been criticised for not as yet acting on its promise.

The state-owned company said however that it needed the new locomotives regardless of the electrification issue to replace ageing engines in its fleet.