Hamas has launched an unprecedented attack against Israel. Here's what to know

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A large-scale surprise attack by Gaza militants on Israel has left hundreds of Israelis dead, prompting vows of retribution from Israeli Prime Minister Benjamin Netanyahu and a lethal volley of retaliatory Israeli airstrikes.

"Citizens of Israel, we are at war - not in an operation, not in rounds - at war," Netanyahu said in a video message shortly after the militant group Hamas, which controls the coastal enclave of Gaza, fired a barrage of rockets and sent gunmen into Israel on Saturday in a multi-pronged and unprecedented attack in the long-running conflict.

By nightfall, Israeli air strikes on Gaza had killed hundreds of Palestinians and wounded over 1600, according to local health officials.

Still unknown are the fates of several hostages, including Israeli soldiers, that Hamas claims to have captured.

Here's what we know so far.

Around 6:30 a.m. local time on Saturday, when many Israelis were likely to have been asleep, sirens were heard as far north as the Tel Aviv area, east to Beer Sheba, and many other locations in between as rockets flew over Israel.