The airstrikes - which started at 1.14am on Monday from armed drones - took out a target in the centre of Jenin's refugee camp, close to UN-funded schools.

Israel's military described the target as a Joint Operations Centre "used as an advanced observation and reconnaissance centre, a place where armed terrorists would gather before and after terrorist activities, a site for armament of weapons and explosives, and as a hub for co-ordination and communication among the terrorists".

Further strikes have followed in what is one of the biggest West Bank incursions in 20 years.

At least eight Palestinians have so far been killed and more than 50 wounded - 10 of them critically, according to the Palestinian health ministry.

Three minutes after the initial airstrikes, at 1.17am, ground troops entered and started moving through buildings focusing on infrastructure, seizing weapons and targeting command and control.

In a separate incident, a 21-year-old Palestinian was killed by Israeli fire near Ramallah, the ministry said.

There have been no reports of Israeli casualties yet.

"We are acting against specific targets," said the international spokesman for the Israel Defence Forces (IDF), Lt Col Richard Hecht, in an early morning briefing.

"We're not here to hold ground. The focus is breaking the perceived safe-haven for terrorists. We will do it for as long as needed."

It's thought around 2,000 Israeli soldiers are taking part.

Residents have reportedly been sent texts urging them to stay indoors and some members of militant groups have been told to lay down arms and surrender.

People in the camp said power was down in some areas and bulldozers had damaged buildings as they cleared the way for Israeli forces.

The Palestinian Authority and Jordan have been informed and messages sent through back channels to Hamas and Palestinian Islamic Jihad in the Gaza Strip warned them not to get involved.

Palestinian President Mahmoud Abbas has suspended contact and security coordination with Israel in response to the attacks.

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A statement from the Joint Chamber of Palestinian Resistance called on people to "activate the confrontation with the occupation, support Jenin, and teach the enemy harsh lessons in response to its aggression".

The Jenin Brigades, a unit made up of militant groups, said it was battling Israeli forces and had shot down one of the drones.

There has been speculation for weeks that the IDF might carry out a more sustained operation in the West Bank after one of the deadliest years for decades.

Members of the Netanyahu government had urged the prime minister to approve a wide scale operation across the Occupied Territories, but it seems he has opted for a more limited operation in Jenin, which has been the centre of terrorist activity in recent months.

The use of airstrikes in the West Bank is extremely rare - two weeks ago an Apache helicopter fired into Jenin during violence between Israeli soldiers and Palestinian militants.

It was the first time airstrikes had been used since the Second Intifada, almost 20 years previously.