Israel said its air force had attacked “about 175 terrorist targets” in Gaza and Lebanon over the past day.
The Hamas-run government media office said the bombing in Beit Lahia on Saturday night hit “crowded” residential areas, and that 73 people had been killed – a number also reported by Gaza’s civil defense agency. The BBC cannot independently verify the figures.
According to Palestinian news agency Wafa, an entire residential complex was destroyed in the strikes.
Rescue efforts in Beit Lahia are currently hampered due to communications and internet services being severed in the region, Gaza health officials added.
The latest strikes come just hours after reports of heavy gunfire from Israeli troops at the Indonesian Hospital in the city.
The Israel Defense Forces (IDF) told the BBC it had struck a “Hamas terror target” and was “doing everything possible to avoid causing harm to civilians.”
It said the casualties given by the Hamas office were “exaggerated” and said such sources had “proven to be sorely unreliable in previous incidents.”
Israel began a renewed military offensive in northern Gaza in early October, saying it is trying to prevent Hamas from regrouping in the area.
In particular, Israeli forces have surrounded and bombarded the densely-populated Jabalia area, which includes an urban refugee camp – with at least 33 people reported killed in a strike late on Friday.
Humanitarian groups have warned that virtually no aid has entered the area in the past few weeks. Israel’s own statistics show that aid deliveries to Gaza as a whole have collapsed when compared with the same period in September.
The UN’s top humanitarian official, Joyce Msuya, said on Saturday that Palestinians in northern Gaza are enduring “unspeakable horrors” and called for these “atrocities” to stop.
Israel has repeatedly denied it is preventing humanitarian aid from entering Gaza but the US has told it to boost access or risk having some American military assistance cut off.