A teenager who sped through Southland at 141km/h in foggy, wet conditions this morning told police he was "running late for school".

The 16-year-old was driving his mother's Subaru at the intersection of Riversdale-Waikaia Rd and Two Chain Rd when police recorded the speed.

Riversdale Senior Constable Adam Roberts told Fairfax the boy's actions were "incredibly dangerous".

The driver had his licence suspended for 28 days and was fined $510.