The riders were spotted just south of the Remutaka Hill Road on Saturday.

A pair of motorcyclists hit speeds of more than 300kmh as they tore through Upper Hutt.

Two Japanese 1000cc sports bikes were spotted about midday on Saturday on State Highway 2 south of the Remutaka Hill where they were clocked at 247kmh, police said.

As they sped off, they reached speeds of more than 300kmh posing "unimaginable" risks to themselves and other road users, Wellington road policing senior sergeant Thomas McIntyre said.

"At 247kmh, the riders would have been travelling at just under 70 metres per second — had they crashed they would have killed themselves and possibly other road users."

Police have appealed for information to find the motorcyclists.