After eight days of massive bombardment, Israel sent its ground troops into the besieged, bombed-out Gaza Strip late on Saturday, January 3.
"Large numbers of forces are taking part in this stage of the operation including infantry, tanks, engineering forces, artillery and intelligence with the support of the Israel air force, Israel navy, and other security agencies," the Israeli army said in a statement.
Residents in the town of Beit Lahiya said Israeli tanks opened fire shortly after crossing the border.
They also said Apache helicopters were backing up ground troops taking part in the operation.
Witnesses said there were explosions and tank fire just north of Jabaliya where Israeli troops had moved several hundred meters (yards) into the territory.
Gaza emergency services said one child was killed and 11 other children were wounded, the first victims of the ground offensive.
They said two other Palestinians, including a woman, were killed east of Gaza City.
Thousands of Israeli troops and tanks had encircled Gaza as artillery lobbed shells ahead of the offensive.
In one of the deadliest single strikes, an Israeli jet hit a mosque in the northern town of Jabaliya, killing at least 16 people among more than 200 people at prayer.
Four children — two brothers aged 10 and 12 and two cousins under 16 — were among the dead at the Ibrahim al-Maqadna mosque.
Eight days of massive Israeli bombardment have killed at least 460 Palestinians, wounded more than 2400 an caused widespread destruction.
The Israeli army said ground military operations in Gaza will last "many days."
"The combat will last many days," it said a statement.
Palestinian resistance fighters were night-time battles with the invading Israeli troops.
A senior Hamas official said they had killed a number of the advancing Israeli soldiers but there was no word from Israel on any casualties.
"We have received credible information that tens of the advancing Israeli soldiers have been killed and wounded by our fighters," Mohammed Nazal told Al-Jazeera TV.
"Your incursion into Gaza will not be a walk in the park and Gaza will become your cemetery God willing," Hamas spokesman Ismail Radwan said earlier in a televised speech.
"You do not have any other choice but to unconditionally end the aggression and lift the blockade," he said.
"You will not enjoy security as long as our people don’t have any," he said, addressing Israelis.
Earlier, Ezzedine Al-Qassam Brigades, the military wing of Hamas, threatened Israeli troops with "a high price for its operation in northern Gaza Strip."
Hamas leader Khaled Meshaal stressed a day earlier that his group remains strong and will emerge victorious from the current military confrontation with Israel.
He threatened Israeli soldiers who invade Gaza that they risk being taken prisoner by the resistance groups just like their colleague Gilad Shalit, captured in 2006.
(IslamOnline.net and Agencies)