Most of the victims, including women and children, are from the same family, the source at the Harish hospital said, adding that three people were left critically wounded by the bombing conducted last evening.
It was not immediately clear who carried out the strike.
The attack has not been claimed by forces loyal to strongman Khalifa Haftar, which have been besieging Derna for months and regularly conduct air strikes against the eastern city.
Derna, some 900 kilometres (560 miles) east of Tripoli, was known for being a bastion of jihadists even before the 2011 uprising that toppled and killed longtime dictator Moamer Kadhafi.
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Jihadists in the conflict-torn country have frequently accused Haftar's main international backers, Egypt and the United Arab Emirates, of participating in deadly raids.
Egypt in late May said it launched strikes in the region of Derna after a bloody attack on its soil claimed by the Islamic State group that left 29 people dead.
Controversial strongman Haftar supports an administration based in the country's east that has refused to recognise the UN-backed Government of National Accord based in Tripoli.