Local officials reported casualties and television pictures showed smoke pouring from a building.
“The IDF is currently striking in the Gaza Strip. A special situation has been declared on the Israeli home front,” the military said in a statement.
A spokesman for the Gaza Health Ministry said there had been a number of casualties and a state of emergency had been declared. Television pictures showed black smoke rising from the roof of a building in the heavily populated strip.
The strikes came after Israel arrested Bassam al-Saadi, a senior leader of the Palestinian Islamic Jihad group, during a raid in the occupied West Bank city of Jenin earlier this week.
It subsequently closed off all Gaza crossings and some nearby roads over fears of retaliatory attacks from the group, which has a stronghold in Gaza.
“The enemy has begun a war against our people and against us and we will defend ourselves and our people,” the Islamic Jihad said in a statement.