The armed wing of the Palestinian Hamas movement has said it is ending its five-month truce with Israel.
This is the first time Hamas has fired rockets into Israel in five months
Earlier in the day the militant group launched a sustained barrage of rockets and mortars into Israel, the first such attack since November.
The group, the Izzedine al-Qassam Brigades, said the attacks were in revenge for recent killings of Palestinians by Israeli forces.
The ending of the truce has not been confirmed by Hamas political leaders.
The Palestinian prime minister, Hamas's Ismail Haniya, whilst not confirming that the ceasefire was over, said the Palestinians had tried hard to observe the truce, but this had been undermined by what he called Israeli aggression.
An Israeli spokesman said only a small number of rockets landed in Israeli. There were no reports of casualties.
The attacks came as Israel celebrated the 59th anniversary of its establishment as a modern independent state.
Hamas's military wing said the attack, of nearly 100 rockets and mortars, was a response to the killing of nine Palestinians, five of them believed to be militants, during Israeli military operations in the West Bank.
Israel helicopter gunships fired machine guns near the border fence in southern Gaza soon after the rocket fire, Palestinian witnesses reported.
Hamas, which won parliamentary elections last year and is the leading faction in the Palestinian Authority, agreed to a ceasefire in November.
But it reserved the right to respond to the killing of Palestinians by Israeli forces.
A spokesman for the Izzedine al-Qassam Brigades told the BBC that the idea of a truce had become an illusion.
A spokesman for Hamas's armed wing, Abu Ubeida, said: "There is no truce between us and the occupation, the occupation destroyed the truce from the moment it started, we did not trust the intentions of the occupation from the beginning."
The truce had been largely observed since November, despite some violations on both sides.
BBC Middle East correspondent Katya Adler says there has been tension within Hamas over how far the ceasefire should hold.
An Israeli government official said there have been rocket attacks from Gaza into Israel at least every two days.
There is speculation in Israel that it might taken more concerted military action into Gaza.
Mark Regev, spokesman for the Israeli foreign ministry, said: "Israel is not interested in escalation, but we hope that cooler heads among the Palestinians prevail. We however reserve the right to protect and defend our civilians."