Reports are coming in of a blockage on State Highway 29A near Barkes Corner.

A caller to the 0800 SUNLIVE news hotline says there is a police car blocking the highway.

"Traffic is being diverted through Greerton."

NZTA Waka Kotahi has issued an alert saying due to a gravel spill, the westbound lanes of SH29A are blocked between Pyes Pa Road roundabout and Takatimu Drive roundabout.

"Expect delays in the area. Follow directions of emergency services."