It was not immediately clear whether the tunnel was one used for smuggling goods over the Egyptian border or a shaft intended for infiltration and attacks against Israel.
Tunnel deaths have been a common occurrence in the Strip.
In February three Palestinians died in a smuggling tunnel between Gaza and the Sinai Peninsula after inhaling toxic gas while conducting repair work. Several Hamas members have been killed in collapses since the beginning of the year.
Last year, 22 members of Hamas’s armed wing were killed while “preparing equipment,” the group has said, the majority in a string of tunnel collapses.