Six Palestinians broke out of an Israeli prison Monday through a tunnel dug beneath a sink, triggering a massive manhunt for the group that includes a prominent ex-militant.

The Israel Prison Service said an alert was sounded at roughly 3:00 am (0000 GMT) by locals who spotted "suspicious figures" outside the Gilboa prison in the country's north.

The group includes Zakaria Zubeidi, a prominent former militant leader from the flashpoint city of Jenin in the occupied West Bank, the IPS confirmed in a statement.

Police, the army and agents from Israel's powerful internal security agency the Shin Bet joined the search effort, officials said. Sniffer dogs were deployed and checkpoints set up in the area surrounding Gilboa.

Israeli media reports said it was possible the escapees had already returned to the West Bank, a territory occupied by Israel since 1967.

The army said its forces were "prepared and deployed" in the West Bank as part of the operation.

In footage that recalled the iconic 1994 prison escape film "The Shawshank Redemption," the IPS released a video which showed agents inspecting a narrow tunnel dug beneath a sink, burrowing deep into the ground.  

The jail break occurred hours before Israel begins its High Holiday season, starting with Jewish New Year which begins at sundown.

Israeli Prime Minister Naftali Bennett in a statement called the escape "a serious incident" and said he was receiving regular updates about the search.

All 400 inmates detained at Gilboa over "security offences" are being relocated in case additional tunnels have been dug beneath the facility, according to the IPS.

Gaza groups cheer

Hamas, the Islamist group that controls the Israeli blockaded Gaza Strip, called the escape a "courageous and heroic act" and a "real defeat" for Israel's security system.

Islamic Jihad, one of Gaza's most powerful armed groups after Hamas, lauded the jail break as "a powerful blow to the occupation forces".

Zubeidi was the former head of the Al-Aqsa Martyrs' Brigades and a well known figure among Palestinians and Israelis.

He was arrested over "terror allegations" in 2019 in a West Bank village near Ramallah.

He had faced charges in the past from the Palestinian Authority for taking part in a shooting attack on the residence of Jenin governor Qaddura Musa in 2002.

Musa died after suffering a heart attack during the incident, and Palestinian security forces arrested dozens of people, including Zubeidi, shortly afterwards.

Zubeidi in 2007 agreed to lay down his arms and went on to help found Jenin's Freedom Theatre.

In 2011, the Freedom Theatre's well-known Israeli-Palestinian director Juliano Mer-Khamis was gunned down in Jenin's refugee camp, in an attack that remains unsolved.