Eleven people were injured, two seriously, in the early-morning blast that caused the three-story building to collapse, the Times of Israel reported.
Officials said the first two bodies, a couple, were discovered soon after the explosion. The three bodies -- a husband, wife and their son -- were found several hours later.
Initial reports indicated a gas tank explosion may have been the cause, the Times said. Police, however, said they were investigating the possibility of sabotage.
Witnesses told the Times the building's landlord and the five families who were tenants had a longstanding dispute over erecting cellular antennas on the building. The Times said sabotage attempts had been made before.
Public Security Minister Yitzhak Aharonovich, who visited the scene, said all possibilities would be examined.
"It's possible this was a localized incident or a criminal act, but we must be patient," he said.