Israeli warplanes retaliating for rocket fire from the Gaza Strip pounded dozens of security compounds across the Hamas-ruled territory in unprecedented waves of airstrikes Saturday, killing more than 200 people and wounding nearly 400 in the single bloodiest day of fighting in years.

Many of those killed were security men, but an unknown number of civilians were also among the dead.

Hamas said all of its security installations were hit, threatened to resume suicide attacks, and sent at least 70 rockets and mortar shells crashing into Israeli border communities.

One Israeli was killed and at least six people were hurt.

In Gaza City's main security compound, bodies of more than a dozen uniformed Hamas police lay on the ground.

The Gaza police chief was among those killed.

Gaza health official Moaiya Hassanain said by early evening, 205 Gazans were known to be dead and 388 wounded.

The offensive began eight days after a six-month truce between Israel and the militants expired.

During that time, the military says, rocket and mortar squads have fired 200 projectiles at Israeli targets, and in recent days, Israeli leaders had been voicing strong threats to launch a major offensive.

Defence Minister Ehud Barak said Israel would expand the operation if necessary.

Top aide to Palestinian President Mahmoud Abbas, strongly condemned the airstrikes.

"In this moment we express our solidarity with all the victims of this aggression and we call for an immediate halt and ending of this aggression against (the) Gaza Strip. Our leadership and our government are taking measures now in order to help the victims of the aggression in (the) Gaza Strip and as well we are having contacts at this moment with all international and Arab concerned parties in order to move quickly for achieving (an) unconditional end of this aggression."

Ismail Haniyeh, Hamas Leader in Gaza vows Hamas will not back down.

"We will not compromise or back down on our religion or cause. If you destroy Gaza, and you will not be able to, because Gaza is too tough to be broken, too hard to be destroyed. If you destroy Gaza and you will not be able to, Gaza will remain in the hearts of millions of this nations sons and daughters. If you kill thousands of us and of our people you will be able to kill our spirit, or our honour, or our dignity, or our resistance, or our loyalty to our martyrs and our wounded and prisoners, or our loyalty to this noble quest."

Meanwhile, protests against Saturday's campaign erupted in Arab Israeli villages, the Abbas-ruled West Bank and across the Arab world.

The most violent West Bank response came in the city of Hebron, where dozens of youths, many of them masked, hurled rocks for hours at Israeli forces, who lobbed tear gas and stun grenades in response.

The international community including the China, the United States, Britain and the United Nations, have all called for an immediate restoration of calm, and the Arab League has scheduled an emergency meeting on Sunday to discuss the situation.

Chinese Foreign Ministry spokesman Qin Gang said China is seriously concerned about the situation in Gaza. China deplores actions that caused civilian casualties, opposes use of force to settle disputes, and calls on parties concerned to exercise maximum restraints and to solve problems through dialogue.