Police have set up a contraflow to allow one lane of traffic in each direction.

Lt. Bennett Martin, supervisor of Honolulu police vehicular homicide investigations, said a tractor-trailer carrying gravel heading toward downtown on Pali Highway crossed the center median for unknown reasons and collided head-on with a Kailua-bound van at about 11:45 a.m.

A second van was also struck while several other vehicles were damaged by debris, said Martin.

According to Honolulu Fire Department spokesman Capt. Emmit Kane, a Handi-Van was among the vans struck by the truck.

The tractor-trailer also knocked down a utility pole, knocking out electrical power to about 1,000 Hawaiian Electric Co. customers for about 45 minutes in the Nu‘uanu area. Heco spokeswoman Pepi Nieva said power was restored at 12:28 p.m.

Donnie Gates, city Emergency Medical Services assistant chief, said four people were taken to The Queen’s Medical Center, one in"extremely critical" condition, another in serious condition and two others with minor injuries. Police said one person died at Queen’s and another was in critical condition.