Israel was taken by surprise by the most ambitious operation Hamas has ever launched from Gaza.

The scale of what's been happening is unprecedented. Hamas breached the wire that separates Gaza from Israel in multiple places in the most serious cross-border attack Israel has faced in more than a generation.

It came a day after the 50th anniversary of the surprise attack by Egypt and Syria in 1973 that started a major Middle East war. The significance of the date will not have been lost on the Hamas leadership.

Israel's Prime Minister Benjamin Netanyahu says his country is at war and will exact a heavy price from its enemies.

Videos and photos of dead Israelis, civilians as well as soldiers, are all over social media.