It was the first major Israeli ground offensive in Gaza in just over five years, and came hours after Hamas militants tried to infiltrate Israel through a tunnel under the Gaza-Israel border, but were stopped by Israel.
Lieutenant Colonel Peter Lerner, an Israeli military spokesman, said the operation is open-ended.
“We will be striking the infrastructure,” he said. “We will be striking the operatives in order to safeguard the civilians of the state of Israel especially issues to do with tunnelling, that was exemplified earlier today.”
Thousands of Israeli soldiers had massed on the border with Gaza in recent days, waiting for the order to go in.
The operation followed a brief truce earlier yesterday in which Israel held fire to allow Gazans to stock up on food and other necessities after being largely holed up at home since the conflict began last month.
Israeli strikes have hit more than 2,000 targets in Gaza. Hamas launched nearly 1,500 rockets at Israel, the Israeli military has said.
Israeli Prime Minister Benjamin Netanyahu’s office said he instructed the army to go ahead after Hamas rejected an Egyptian ceasefire plan earlier in the week and after Hamas militants tried to infiltrate Israel through a tunnel from Gaza.
“In light of the despicable and relentless aggression by Hamas and the dangerous infiltration into Israel, Israel is obliged to protect its citizens,” the statement said.
Israel last carried out a major ground offensive in Gaza in January 2009.
Security officials reported heavy Israeli shelling in eastern Gaza, near the border with Israel.
During the earlier humanitarian ceasefire, Gaza residents rushed to restock supplies after more than a week of being mostly holed up at home for fear of airstrikes.
“The situation is likely to get worse because there is no clear way out of it,” said Moussa Amran, 43, in central Gaza City.
The city’s streets returned to normalcy during the lull, with traffic jams, motorists honking horns, and police directing traffic at busy intersections.
Hundreds lined up outside banks, with people jostling and shouting to get to ATMs.
Abdallah Jaber, 42, seized the opportunity to visit his 87-year-old father, Hosni, in a care facility for the elderly and disabled close to the Israeli border, in an area that has been targeted repeatedly by the Israeli army as a launching area for rockets. Several tank shells hit the upper floors of the five-storey Wafa rehabilitation centre last week, punching large holes into the wall facing the border.