Israel has watched the rapid overthrow of the government of Syrian President Bashar al-Assad with a mixture of hope and concern as officials weigh the consequences of one of the most significant strategic shifts in the Middle East in years.

Prime Minister Benjamin Netanyahu hailed the ousting of Assad as an "historic day" that followed the blows delivered by Israel against Assad's supporters Iran and Hezbollah in Lebanon that had created a chain reaction throughout the region.

"This of course creates new, very important opportunities for the State of Israel. But it is also not without risks," he said on a visit to the border area on Sunday.

Israel has pushed tanks over the border into the buffer zone with Syria to prevent a spillover from the turmoil there, but has declared its intention of staying out of the conflict engulfing its neighbor.

Netanyahu said Israel was working on a policy of "good neighborliness" and would "extend a hand of peace" to Druze, Kurds, Christians and Muslims.

"We will closely follow developments. We will do what is necessary to protect our border and protect our security," he said in a filmed statement.

The lightning advance of Syrian rebel forces since their seizure of Aleppo last week has thrown further turmoil into a region already reeling from the shocks of the war in Gaza and Israel's subsequent campaign against the Iranian-backed Hezbollah movement in Lebanon.

"At the moment, if we aren't attacked we will just retain the current situation," Israel's Consul General in New York Ofir Akunis told Reuters.

"Nobody should think that this threat of the Shiite-Iranian axis of evil has been eliminated entirely, there are changes but we need everyone... to be even more vigilant about this," said Akunis.

Overnight, the Israeli military said it was not interfering with internal events in Syria but would "operate as long as necessary in order to preserve the buffer zone and defend Israel and its civilians."

The rapid collapse of the Syrian government has presented Israel with a mix of problems and opportunity, said Dina Lisnyansky, a specialist in regional politics at Tel Aviv University.

Iran's inability to protect its long-time ally Assad has underlined the weakness laid bare by Israel's devastating campaign against Hezbollah, which left the long-time Iranian proxy reeling, its long-feared missile arsenal largely destroyed and most of its top leadership dead.

But the advance of a disparate group of rebel forces with roots in the Islamist ideology of Al Qaeda risks re-igniting chaos in Syria and creating a new security threat on Israel's borders.

"It really depends on what happens next in Syria," Lisnyansky said. "We need to know if it goes to the peaceful side of events or perhaps whether a new civil war could occur in Syria, which would of course endanger our borders," she said.