Police have released the name of a man killed in a motorbike crash in Waikato on Sunday.

He was 40-year-old Ashley Keith Smith of Northland.

Police said Mr Smith died after losing control of his north-bound Suzuki in wet conditions on the Waikato Expressway near Rangiriri, north of Huntly, about 7pm.

Mr Smith's death was the 38th fatal crash to occur in the Waikato this year and brings the district's road toll to 42 compared to 49 for the same period last year.