Police and emergency services were called to the crash on Glenbrook-Waiuku Rd, south of the city, just before 12.30am today.
It is understood the crash happened at the Caltex service station.
Two people were thrown from the vehicle - a ute - after it collided with the electric sign and rolled, police said.
Three others were initially trapped inside the vehicle.
“All five were taken to hospital and are reported to be in a serious condition,” a police spokeswoman said this morning.
Glenbrook-Waiuku Rd was blocked and diversions were put up in the area for some time.
They have since been lifted and the road was reopened shortly before 6am.