The man said two ambulances, two fire trucks and about five police cars responded to the incident.
He said the teenager was still unconscious when he was taken away by ambulance.
Another resident said the vehicle involved was a white 4X4 ute.
The scene of the incident on Waitaha Rd in Welcome Bay. Photo / Andrew Warner
The 18-year-old was transferred from Tauranga to Waikato Hospital in the early hours of this morning.
A Waikato DHB media spokeswoman said he is still in a critical condition.
Meanwhile, police inquiries into the incident are continuing.
Police would like to hear from anyone who saw a ute driving on Waitaha Rd around 8.45pm last night, or anyone who witnessed the young man falling from the ute.
If you can help, call Tauranga Police on 07 577 4300.