Palestinian health officials said at least 10 people had been killed and several others wounded in an Israeli air strike on a school housing displaced families in Shati refugee camp in Gaza City.
There was no immediate Israeli comment.
As Israeli tanks advanced in Beit Lahiya, a month into a new push on northern Gaza, dozens of families streamed out, arriving at schools and other shelters in Gaza City with whatever belongings and food they could bring.
Drones hovered overhead broadcasting evacuation orders, which were also carried on social media outlets, audio and text messages sent to residents' phones, one displaced man said.
"After they displaced most or all of the people in Jabalia, now they are bombing everywhere, killing people on the roads and inside their houses to force everyone out," the man told Reuters via a chat app, giving only one name, Ahmed, for fear of repercussions.
Israeli forces have carried out several strikes in Lebanon's capital, including near Beirut airport. (AP PHOTO)
Palestinian officials accuse Israel of carrying out a plan of "ethnic cleansing".
Residents say no aid has entered Jabalia, Beit Lahiya or Beit Hanoun since the operation began on October 5.
The Israeli military says it was forced to clear Jabalia and start clearing nearby Beit Lahiya on Wednesday in order to take on Hamas militants who it says have regrouped there.
It denied press reports that people forced to leave northern Gaza would not be allowed to return and said it was continuing to allow aid into northern Gaza and the Jabalia area, where it said it was engaged in "intense combat".
"The statement attributed to the IDF (Israel Defence Forces) in the past 24 hours, claiming that residents of northern Gaza will not be allowed to return to their homes, is incorrect and does not reflect the IDF's objectives and values," it said.
It said 300 trucks of aid from the United Arab Emirates had arrived at the port of Ashdod and would be sent into Gaza via the Erez crossing in the north and Kerem Shalom in the south.
The Israeli military said five soldiers have been killed and 16 wounded in a combat incident in southern Lebanon.
It did not say exactly when the incident occurred.
Overnight on Wednesday, Israel carried out a series of strikes in Beirut's southern suburbs, including at least one just tens of metres from Beirut airport's runways.
Lebanese Transport Minister Ali Hamiye said the airport was functioning normally on Thursday.
Another Israeli strike on Thursday on a car at a Lebanese army checkpoint at the entrance to the southern city of Sidon killed three people and wounded three Lebanese soldiers and four members of a UN peacekeeping contingent, the Lebanese army said in a statement.
A Reuters reporter at the scene said a bus with United Nations markings that was part of a large convoy of Malaysian UN peacekeepers had sustained damage in the strike.
UNIFIL, the peacekeeping force, said in a statement that five newly-arrived peacekeepers were lightly injured in the Sidon drone strike and treated on the spot.
On Wednesday, an Israeli air strike destroyed an Ottoman-era building near the famed UNESCO-listed ancient temples of Baalbek in eastern Lebanon, the region's governor and an organisation that has organised cultural events there said on Thursday.
Governor Bachir Khodr told Reuters the strike hit the empty heritage building in the closest attack yet to the complex of Greco-Roman and Phoenician temples that make up the World Heritage Site, just metres away.
