A man working inside the Highway 99 tunnel in Seattle was injured when he fell 15 feet from a tipping scaffold.

The Seattle Times reports the incident was reported just before 7 a.m. Saturday from the south portal of the tunnel, where people and supplies enter to build the double-deck highway.

Chris Dixon with contractor Seattle Tunnel Partners says the man apparently was installing a roadside wall.

The Seattle Fire Department says the 58-year-old man was taken to Harborview Medical Center in serious but stable condition.

Seattle Tunnel Partners and the state Department of Labor & Industries have started investigations.

Although tunnel boring machine Bertha finished digging in April, 1½ years of work remains until traffic enters in 2019.

Several workers have been hurt during the project but there have been no fatalities.