Police are urging people to slow down on the roads following a double fatal crash on Christmas Day.

Two people died in a single-vehicle crash on Clevedon-Kawakawa Road around 7.30pm.

"This is the second serious single-vehicle crash we've had in Counties Manukau District today," says Inspector Jason Homan.

"In both crashes, high speed appears to have been a factor."

"We don't want to see any more lives lost this holiday period.

"We are pleading with people to slow down, wear your seatbelts, and don't drive if you've been drinking or are fatigued."

A person remains in hospital in a critical condition following a crash on Princes Street East in Ōtāhuhu yesterday morning.