Israel has shelled a newly declared buffer zone in northern Gaza, soon after warning Palestinians they could be shot if they entered it.
Explosions were heard in the buffer zone within minutes of the deadline
The Israeli-imposed restrictions came into effect from 1800 (1600 GMT) and blasts were heard within minutes.
Later, local witnesses also reported an airstrike, but subsequent reports suggested further shelling of the area.
The 2.4 km (1.5 mile) buffer area is designed to stop rocket attacks against Israel by militants.
Palestinian officials earlier rejected the buffer zone proposal and called for Israel to re-engage in meaningful peace negotiations.
"The ways of buffer-zones, militarism, incursions, attacks, assassinations will just ... add to the cycle of violence and counter-violence," said senior negotiator Saeb Erekat in a BBC interview.
Leaflets warning of the impending restrictions and signed by the Israeli army command were dropped from the air over northern Gaza earlier on Wednesday.
They included a map of the security zone and said it will be enforced "until further notice".
"For your own safety, read this statement carefully and act accordingly," the leaflet says in Arabic.
"Know that the terrorists have made you hostages and human shields and safeguard your interests," it continues.
There are no Palestinian villages in the zone, which corresponds to the site of three former Israeli settlements.
Israeli troops and settlers were pulled out of Gaza earlier this year after 37 years of military occupation, but the territory's coastline and airspace, and its borders with Israel, remain under Israeli control.
Israeli Prime Minister Ariel Sharon gave the order to impose the buffer at a meeting with cabinet colleagues and security officials on Sunday.
The move followed talks on Thursday in which the prime minister told the army to do everything possible to stop rocket fire from the territory.
A rocket attack that day wounded four Israeli soldiers.
A Palestinian man was killed when the army responded by firing artillery shells at the launch site in a field it said was empty.
The Palestinian president, Mahmoud Abbas, has asked militant groups to stop firing rockets.
But Islamic Jihad, blamed by Israel for the majority of the attacks, has reportedly rejected Mr Abbas' call, blaming Israel for a recent escalation in violence.
They say the rocket attacks are retaliation for raids in the West Bank, as well as air strikes on Gaza.