It was the most serious flare-up in and around the Gaza Strip since November 2012 and came as Israel struggled to contain a wave of unrest over the grisly murder of a Palestinian teenager by Jewish extremists.
Washington, Brussels and a growing number of Arab states have demanded a halt to the violence, which is threatening to expand into a wider conflict.
Since Operation Protective Edge began early on Tuesday, Israeli warplanes have bombed 430 targets in Gaza, and Hamas militants have hit back with 117 rockets, some of which struck Jerusalem and Tel Aviv and as far away as Hadera, 116km to the north.
So far, 32 Palestinians have been killed, among them militants but also women and children.
So far, neither side has shown any sign of backing down, as Israel stepped up its preparations for a possible ground assault, approving the call-up of 40,000 reservists.
Overnight, Israeli warplanes bombed 160 targets across Gaza, hitting concealed rocket launchers, Hamas command and control centres and many tunnels, military spokesman General Moti Almoz told army radio.
"Over the last two days we attacked a total of about 430 targets. We are at the start of the second day of an operation which is widening," he said.
Israel's security cabinet has ordered the military to "significantly broaden" its assault on Hamas, a minister said on Wednesday.
"We didn't limit the campaign in terms of time, in fact we ordered the IDF (army) to significantly broaden the attacks on Hamas," Interior Minister Gideon Saar told army radio.
"We're ready for every possibility, including a ground operation if necessary, although it's not going to be the first step. But there is a readiness for that and that's why we ordered the call-up of 40,000 reserve soldiers," he said.
The current round of violence began on June 12 when militants in the West Bank kidnapped and murdered three Israeli teenagers, prompting a major crackdown on Hamas, whom Israel blamed for the killings.
In response, militants in Gaza, where Hamas has its stronghold, fired a growing number of rockets over the border, prompting Israel to launch Operation Protective Edge on Tuesday.
What started as an escalation along the Gaza frontier rapidly expanded as night fell with a barrage of rockets on central Israel, where sirens sent thousands bolting for the bomb shelters in and around Jerusalem and Tel Aviv.
The confrontation has drawn sharp condemnation from Washington and Brussels, and the Arab League has called for an urgent UN Security Council meeting on the crisis.
On Wednesday, Jordan, one of just two Arab countries to have signed a peace treaty with Israel, demanded an immediate halt to Israel's "barbaric aggression" in Gaza.
Iran's foreign ministry Wednesday condemned the air raids and called on the West to urge the Jewish state to prevent a "human catastrophe".
