Emergency services are at the scene of a crash on the corner of Heads Rd and Taupo Quay where a van hit a power transformer about 11.15am.
Constable Trevor Scarrow said it appeared the male driver had suffered a medical event.
Emergency services did not want to touch the van because of the live cables underneath it and were waiting for the power company to turn off the power, he said.
"We're talking to him and just waiting for the power company to disconnect things before we continue," Scarrow said.
"He seems to be okay. The ambulance will check him out more thoroughly when the power's disconnected."
Once the power is turned off the road will be reopened to two lanes.
Trains using the nearby rail line have been temporarily stopped.
A St John spokeswoman said one person has been taken to Whanganui Hospital in a moderate condition.