MILTON, WA — Four people were injured in a multi-vehicle crash involving 20 vehicles early Monday on northbound Interstate 5 near the Pierce County line, according to the Washington State Patrol.

Troopers responded around 5:05 a.m. on Jan. 19 near milepost 139 after multiple vehicles struck large metal debris in the roadway. WSP said the initial crashes triggered a chain reaction as other drivers swerved to avoid the debris and stopped vehicles, resulting in additional collisions.

Several vehicles came to rest on both shoulders of the highway. One injured person was transported to a hospital, while three others were treated at the scene. No fatalities were reported.

The roadway was partially blocked for nearly four hours while crews cleared the scene and removed damaged vehicles.

The crash remains under investigation.