Four blasts hit vehicles in Gaza City just after 06:00 (03:00 GMT). Two people suffered minor injuries.
News agencies said the five cars belonged to members of Hamas and the rival Islamic Jihad militant group.
Supporters of the so-called Islamic State group have threatened Hamas' leadership in Gaza in recent weeks.
The Jerusalem Post quoted one Hamas commander, Abu Hamar, as saying IS was to blame for Sunday's explosions. He called for Hamas to respond.
A video posted online last month by IS supporters in Syria made direct threats against what they called "the tyrants of Hamas" and said they would take over Gaza.
In Gaza, some Salafist groups - who adhere to a strict lifestyle based on that of the earliest followers of Islam - have started to support IS.
They have been blamed by Hamas for a series of explosions in the area. Dozens of Salafists have been arrested in recent weeks.
A series of explosions on Sunday targeted cars belonging to officials in Gaza, including those from the ruling Hamas militant group.