A second Gazan was found dead on Sunday after the collapse of a tunnel on the Egypt border, the interior ministry in the Islamist Hamas-run enclave said.
On Thursday, rescue services said seven men had been trapped in the collapse.
Five were rescued, but on Sunday the ministry said they had retrieved the body of Mohammed Abbas of Rafah, after announcing the death of a man named as Fadi Abu Dan.
A local civil defence official described the underground passage from the southern Gaza town of Rafah into neighbouring Egypt as a "trade tunnel".
The cave-in was caused by Egyptian flooding of the border zone in its campaign to stop smuggling, the official told AFP.
Since 26 January, at least 12 Gazans have been killed in five separate tunnel collapses with both Israel and Egypt operating against the diggers.
Egypt has already established a buffer zone 10 kilometres (6.2 miles) long and half a kilometre wide along its border with Gaza.
Palestinians fear such moves will further isolate Gaza, where more than 100,000 were left homeless in last summer's war with Israel.
An Israeli blockade severely restricts the movement of people and goods into and out of the territory, and Egypt's sole border with Gaza has also remained largely closed since 2013.
The passages to Egypt are used for transit of commercial goods, cash, people and, allegedly, weapons.