Palestinian doctors said the eight were killed in Israeli air strikes and exchanges of fire in Gaza City's Shejaiya neighbourhood on Wednesday.
The dead included a 14-year-old boy shot in the chest as he watched the fighting, hospital sources said. At least five other people were wounded in the attacks, they said.
In other incidents, witnesses said two Shejaiya residents, Rami al-Gharabli, 27, and Yasser al-Gharabli, 25, were trying to get out of their house encircled by Israeli tanks when they were shot.
Two other men, Raed Isbita, 23, and Mohand Jindiya, 23, attempted to help the pair when they were shot too.
Another man, Salman Abu Qunbus, 25, was killed in a separate incident in Shejaiya.
According to witnesses, all five were civilians, but the Israeli army said the tanks fired after "armed men approached troops operating in Shejaiya".
Israel also said that some of those killed in Wednesday's clashes "either fired anti-tank missiles or were approaching the [Israeli] forces", an army spokeswoman told AFP news agency.
Also on Wednesday, a Palestinian teenager injured in fighting in Shejaiya on Tuesday died of his wounds, the doctors said.
And a senior leader of Islamic Jihad who was shot by undercover Israeli troops in the West Bank a week ago died in a hospital in Jordan, Islamic Jihad representatives said on Wednesday.
Hosam Jaradat, the leader of Islamic Jihad in the town of Jenin, was shot and wounded on August 23 by Israeli troops hiding in a vehicle, witnesses said at the time.
At least 200 Palestinians and one Israeli soldier have been killed in the Gaza Strip since June 28, when Israel launched a massive offensive to stop rocket attacks and recover a soldier captured by Palestinian armed groups in a cross-border raid that left two other troops dead.
Up to 5,366 people have been killed since the start of the Palestinian uprising in September 2000, most of them Palestinians.