A witness who saw the aftermath of a serious two-car collision in Taupaki, West Auckland described the scene as "gut-wrenching".

Two people were transported to Auckland Hospital in serious conditions following the crash near the intersection of Waitakere Rd and Taupaki Rd.

"Both cars were totalled. It was gut-wrenching. Also when you see about a dozen emergency vehicles you know its bad … [it] wasn't a pleasant sight," a witness said.

Emergency services called to the scene around 4.30pm on Sunday, police reporting a man and a woman were involved.

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Initial reports suggested the woman was trapped in one vehicle with serious injuries and the man had moderate injuries, a police spokeswoman said.

"They will be taken to hospital. Police are at the scene and the road is currently blocked. Motorists are asked to avoid the area," she said.

However, St John reported two ambulances attended, treated both patients and transported them to hospital in serious conditions.

Elsewhere, traffic was heavy on State Highway 1 near Sanson, following a two-car crash earlier this afternoon.

Police were called at 3.30pm after the cars collided at the intersection of the highway and Frecklington Rd.

One car was in the ditch and one went into a paddock.

One person has reportedly sustained serious injuries and has been taken to Palmerston North Hospital.