TEL AVIV, Israel (AP) — Israel launched a massive manhunt in the country's north and the occupied West Bank early Monday after six Palestinian prisoners tunneled out of their cell and escaped from a high-security facility in the biggest prison break of its kind in decades.

The escape marks an embarrassing security breach just ahead of the Jewish New Year, when Israelis flock to the north to enjoy beaches, campsites and the Sea of Galilee. The prisoners appear to have gone into hiding and there was no indication Israeli authorities view them as an immediate threat.

Palestinians consider prisoners held by Israel to be heroes of their national cause, and many celebrated the escape on social media. Efforts to capture the escapees will likely draw attention to the Palestinian Authority’s security coordination with Israel, which is deeply unpopular among Palestinians. There was no immediate comment from the PA, but President Mahmoud Abbas’ Fatah party praised the escape.

Israeli officials said they have erected roadblocks and are conducting patrols in the area. Israel's Army Radio said 400 prisoners are being moved as a protective measure against any additional escape attempts. The radio said the prisoners escaped through a tunnel from the Gilboa prison, just north of the West Bank, which is supposed to be one of Israel's most secure facilities.

A photo released by the prison service showed a narrow hole in the floor of a cell, and Israeli security forces could be seen examining a similar hole on a stretch of gravel just outside the walls of the prison.

It appeared to be the biggest Palestinian escape from an Israeli prison since 1987, when six militants from the Islamic Jihad group broke out of a heavily guarded prison in Gaza months before the outbreak of the first intifada, or Palestinian uprising against Israel.

Israeli Prime Minister Naftali Bennett called it a “grave incident” that required maximum effort by Israel’s various security branches.

He said he was receiving constant updates on the prison break, which occurred just hours before Israel was to mark the Jewish New Year. There were no instructions for people to alter their routines.

Israeli media quoted Public Security Minister Omer Barlev as saying that extensive planning went into the escape and that the prisoners likely had “outside assistance.” Palestinian prisoners are believed to use smuggled cellphones to communicate with people outside, and the escapees may have arranged for a getaway vehicle.

Police commander Shimon Ben Shabo said officials have reinforced emergency response call centers in the area to respond to any reports about the prisoners and there are “forces available to arrive at any location.”

The escapees are suspected of having headed back to their hometown of Jenin, in the occupied West Bank, about a 25 kilometer (15-mile) drive away. The internationally recognized PA wields little control in the town, where militants in recent weeks have clashed with Israeli forces. Israeli helicopters were seen flying over Jenin on Monday morning.

The Palestinian Prisoners’ Club, which represents both former and current prisoners, identified the men as ranging in age from 26 to 49 years old.

The most well-known is Zakaria Zubeidi, 46, who was a prominent leader in the Al-Aqsa Martyrs Brigade, an armed group affiliated with Fatah, during the second intifada from 2000-2005. He was later granted amnesty along with other Fatah-affiliated militants, but was arrested again in 2019 on what Israeli authorities said were new terror suspicions.

As a child, Zubeidi had been part of a children's theater troupe in Jenin established by Arna Mer-Khamis, an Israeli rights activist, that was the subject of a 2004 documentary.

The other five prisoners were members of Islamic Jihad, and the prisoners' group said four were serving life sentences.

Hundreds of Islamic Jihad supporters rallied in Gaza, and the militant group sent incendiary balloons across the frontier into Israel in support of the escaped prisoners.

“This is a great heroic act, which will cause a severe shock to the Israeli security system,” said Daoud Shehab, a spokesman for Islamic Jihad.

Fawzi Barhoum, a spokesman for the militant Hamas movement that rules Gaza, said the escape shows “that the struggle for freedom from the occupier is continuous and extended, inside prisons and outside.”

Even Abbas' Fatah party praised the escape, with an official Twitter account posting a picture of Zubeidi and hailing what it called the “freedom tunnel.”

The escape poses a dilemma for Abbas, who met with Israeli Defense Minister Benny Gantz a week ago in the first high-level meeting between the two sides in years. Abbas has said he hopes to revive the peace process after more than a decade-long hiatus under former Israeli Prime Minister Benjamin Netanyahu.

But Abbas' PA is deeply unpopular. He canceled the first elections in 15 years in April when it appeared his Fatah party would suffer an embarrassing defeat. The Palestinian Authority was largely sidelined during the Gaza war in May, and it has cracked down on a wave of protests following the death of an activist in PA custody in June.

PA security forces coordinate with Israel to target Hamas and other militants that both view as a threat. But any effort to help Israel re-arrest the escaped prisoners risks further undermining the PA in the eyes of Palestinians.

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Krauss reported from Jerusalem. Associated Press writers Josef Federman in Jerusalem, Jack Jeffery in Ramallah, West Bank, and Wafaa Shurafa in Gaza City contributed to this report.

Laurie Kellman And Joseph Krauss, The Associated Press