A police spokeswoman said the road reopened by 6.30am.
State Highway 51 was closed on Thursday night after a serious two-car crash in Clive.
Emergency services were alerted about 7.50pm to the crash on State Highway 51 north of the intersection with Farndon Rd.
One person was taken to hospital in a moderate condition, and two more in a serious condition.
Another person injured had not left the scene by 9.20pm.
NZTA said SH51 reopened between Farndon Rd and the Ngaruroro River bridge about 9.05pm.
Earlier on Thursday, a serious crash along State Highway 2 near Dannevirke left two people critically injured.
Police were notified of the two-vehicle collision about 1.40pm.
A Hato Hone St John spokesperson said three patients were assessed.
“Two of these patients, both in critical condition, were airlifted to Palmerston North Hospital. The third patient, in minor to moderate condition, was transported by road to Palmerston North Hospital.”
A police spokeswoman said the road reopened at 5.48pm.