Kwon Tae-won, 55, Choi Jae-mun, 59, and Kim Bok-hoi, 58, were found dead hours after the 7:18 a.m. accident, in which the arch of the tunnel collapsed due to an apparent weakening of the earth caused by recent rains.
Forty people were working at the site, but most of them escaped the heaps of falling rock.
The five injured workers were taken to two nearby hospitals.
Jeon Hyun-young, a civil engineer rescued 35 minutes after the collapse, sustained fractures on his legs.
The tunnel, measuring 50 meters high, 50 meters wide, and 240 meters long, is being dug through a mountain to accommodate a four-lane highway.
