Following the worst outbreak of violence along the Gaza frontier since an eight-day war in 2012, the Israeli military said a ground invasion of the enclave was possible, though not imminent, and urged citizens within a range of 25 miles of the coastal territory to stay close to bomb shelters.
Defence Minister Moshe Yaalon said: "We are preparing for a battle against Hamas which will not end within a few days.
"We will not tolerate missiles being fired at Israeli towns and we are prepared to extend the operations with all means at our disposal in order to keep hitting Hamas."
At least six Palestinians were killed and about 25 wounded in one Israeli attack on a house in the Gaza Strip.
Residents said the house belonged to the family of a Hamas member and the casualties occurred when it came under attack for the second time yesterday.
The Israel-Gaza border heated up last month after Israel's arrest of hundreds of Hamas activists after three Israeli youths went missing.
More than 200 rockets have been launched at Israel from the Gaza Strip since Israel mounted the dragnet while searching for the teenagers who were found dead last week.
Israel has accused Hamas militants of killing them. In a suspected revenge attack, a Palestinian teenager was abducted last Wednesday. His charred body was found in a forest and six Israeli suspects have been arrested.