A multi-vehicle rollover crash shut down northbound lanes of the 405 Freeway near Santa Monica Boulevard on Thursday, Aug. 13, backing up morning commute traffic as far south as the 105 Freeway and trapping four people inside an overturned vehicle.

The crash was reported to the California Highway Patrol around 7:25 a.m. in West Los Angeles, according to MyNewsLA. KTLA reporter Tony Kurzweil, who covered the scene from the station's Sky5 helicopter, reported the crash occurred "shortly before 7:30 a.m." Two cars overturned, with one left blocking the slow lane and prompting a large emergency response.

Four people were freed from one of the overturned vehicles, MyNewsLA reported, citing CHP. No one was seriously injured. At least one person declined hospital transport.

SigAlert and lane closures

CHP issued a SigAlert shortly after 8 a.m. for the closure of lanes 4, 5 and 6 on northbound I-405. The alert was extended at 8:30 a.m. for an additional 30 minutes covering lanes 5 and 6.

The backup stretched roughly 20 miles, reaching the 105 Freeway to the south, according to Patch. Sky5 aerial footage captured around 8 a.m. showed vehicles attempting to exit the freeway amid gridlock.

The northbound 405 near Santa Monica Boulevard is a primary artery for Santa Monica residents commuting toward the San Fernando Valley and downtown Los Angeles.

All lanes reopened

All northbound lanes reopened Thursday morning, according to the Westside Current. CHP had not issued a formal press release on the incident as of Thursday morning, and the cause of the crash remains under investigation.

Anyone with information about the crash can contact CHP's West Los Angeles office at 310-477-6100.