Hamas fired dozens of rockets towards Tel Aviv late on Tuesday in response to an Israeli air strike that had flattened a tower block in the Strip.
Israel has launched air strikes against militant targets in the Gaza Strip, after rockets were fired from the territory towards Jerusalem.
The Hamas-run Palestinian health ministry in Gaza said 20 people, including children, had died in the strikes.
In Jerusalem, the rocket fire caused Israel's parliament to be evacuated as sirens sounded.
Tensions between Israel and the Palestinians spiralled in recent days.
Gaza's Hamas rulers had threatened to strike after hundreds of Palestinians were injured in clashes with Israeli police in Jerusalem on Monday.
From Brexit breaking news to HD movie trailers, The Sun newspaper brings you the latest news videos and explainers from the UK and around the world.
Become a Sun Subscriber and hit the bell to be the first to know
Read The Sun: www.thesun.co.uk
Like The Sun on Facebook: www.facebook.com/thesun/
Follow The Sun on Twitter: twitter.com/TheSun
Subscribe to The Sun on Snapchat: www.snapchat.com/discover/The_Sun/1633225139