The bodies of three Palestinians were discovered on Friday after an underground tunnel from the southern Gaza Strip to Egypt collapsed, authorities in the Islamist Hamas-controlled enclave said.

"Civil defence teams found three bodies under the ground near the border, south of Rafah" city after part of the tunnel collapsed on Thursday, interior ministry spokesman Iyad al-Bozom said in a statement.

The deaths occurred after gas was sent into the tunnel from the Egyptian side, triggering the collapse that killed "three workers", a source close to Hamas said on condition of anonymity.

Israel says a tunnel network was dug under the border with Egypt to allow the Iran-backed Hamas and its Islamic Jihad allies to smuggle in arms.

Palestinians say the tunnels were a way for people and day-to-day supplies to get in and out of the coastal enclave, which has been under Israeli blockade since 2007.

Egypt, facing a jihadist insurgency in the Sinai Peninsula neighbouring Gaza, has destroyed hundreds of tunnels since 2013, though some are still being used for smuggling, according to Palestinian sources.

Israel has also destroyed tunnels between Gaza and its own territory.

Throughout an 11-day conflict with armed groups in the enclave in May, Israel said a prime target was the "metro" tunnel network that allowed Hamas militants to launch thousands of rockets.