Police are investigating a fatal crash early Monday on the H-1 freeway in Manoa.

The crash occurred just before 4:15 a.m. on the westbound lanes of freeway between the University Avenue on-ramp and Wilder Avenue offramp.

Lt. Ben Moszkowicz of the Honolulu Police Department’s Traffic Division said an unknown male driver of a silver 2000 Toyota pickup truck was traveling westbound on the freeway when he lost control and struck a concrete median.

A male passenger described to be in his 30s was in the bed of the truck when he was thrown upon impact. He then struck a fence post and landed on the roadway.

Moszkowicz said a white 2014 Nissan minivan operated by a 21-year-old man traveling in the same direction didn’t see the man lying on the roadway and struck him.

The man who was thrown from the pickup truck died at the scene.

Police said the Toyota pickup truck driver fled on foot and remains at-large. He is described as about 5-foot-10 to 5-foot-11 and 170 to 180 pounds. He was wearing a black hoodie and jeans at the time of the crash.

Emergency Medical Services treated and transported a 23-year-old female pickup truck passenger to a hospital in serious condition after she sustained a head injury in the crash.

Police temporarily shut down the westbound lanes of the freeway to investigate.

Moszkowicz said police are continuing their investigation on what occurred prior to the crash and how the male passenger ended up in the bed of the pickup truck.

There were reports of an initial collision between the pickup truck and a silver 2018 Toyota Camry and that a male passenger from the sedan allegedly had jumped into the bed of the truck when the truck attempted to flee.

“I don’t believe it was a collision between the two vehicles. I believe there was damage done but I don’t believe it was (from) a collision,” Moszkowicz said.

Speed may have been a factor in the crash on the part of the pickup truck driver. Police said it’s unclear at this time whether alcohol or drugs were involved.

This is the 20th traffic-related fatality on Oahu compared with 17 at the same time last year.

Anyone with information on the pickup driver is asked to call the Honolulu Police Department’s Traffic Division at 723-3413.