A two-truck crash on the Hume Highway may have been caused by a base jumper on a nearby bridge, according to reports.
Emergency services were called to the Nepean River Bridge following reports that someone had jumped from the structure on Thursday morning although they have not been able to find the man.
Witnesses told police that he was wearing a backpack, prompting an investigation into the possibility of him being a base jumper.
Shortly afterwards, two trucks travelling southbound near Douglas Park crashed, leading to heavy traffic queued around 10km.
Both drivers escaped injury, although emergency services and traffic crews remain on site.
The Nepean River Bridge is frequently used by base jumpers.