It's not known which type of missile was fired into the sea.
The Gazan rocket hit a factory in Ashkelon on Saturday night.
A factory in Ashkelon was damaged even though "only" one rocket was launched from northern Gaza.
IDF Aircraft and Tanks Attack Hamas Underground Infrastructure, Military Positions, in Retaliation for Rockets
Two rockets were fired 20 minutes apart from Gaza at Ashdod and the lowlands under the cover of the stormy weather Saturday night and landed in open areas.
The second rocket landed in an open area in the Ashkelon Coast Regional Council district, according to security sources.
Thousands of families were sent racing for bomb shelters, grabbing sleeping children out of their beds on the way.
The Red Alert incoming rocket siren was triggered in the communities of Nahal Oz, Kfar Aza and Sa’ad.
There were no immediate reports of casualties.
The Jewish community of Kerem Shalom was sent racing for cover when the Red Alert siren was activated.
The injuries followed a rocket that landed in the city center while the peace signing ceremony was in progress in Washington, DC.
The Islamic Jihad announced that the early morning rockets were shot as part of the terror group's "bomb for bomb" equation.
All the injured were taken to Assuta Medical Center in Ashdod, according to MDA.
The IDF said the alarm was triggered only in one community.
On Saturday, Hamas officially protested UN mediator Nickolay Mladenov statement that launching rockets and incendiary balloons at population centers was a violation of international law.
If only Israel had a strong army that could protect it from gangs of Arab thugs. It really should have started one.
We now have a continuous chain of retaliations and counter-retaliations, with both sides invested in not missing a beat lest they appear weak and conciliatory. This will probably go on for a while.
Say what you will about Defense Minister Benny Gantz, this week he appeared to have a backbone.
The three rockets were all neutralized within Gazan territory by the IDF, and landed in the enclave.
“Hamas should know that this is not a game. The time will come when they have to decide, and if they want war they will get war.”
In response to the rocket launches, IAF fighter jets attacked Hamas terrorist targets in the southern Gaza Strip, among them a military rocket storage compound.
Five people were hurt in the attack, including two who suffered from shock.
Jewish residents throughout the district heard the impact as the Iron Dome fighters shot the rocket out of the sky above.
About half a dozen southern Israeli communities were affected along the border of Gaza.
Israeli combat helicopters targeted a Hamas military post in the area of Zeitoun, east of Gaza City.
All the rockets landed in open areas except one that was headed for a populated area -- that one was intercepted by IDF Iron Dome fighters.
"We hold Hamas responsible for all acts of terror emanating from Gaza."
One of the rockets slammed into a children’s playgroup in the yard of a school, causing great damage but miraculously no physical injuries.
The specially-equipped room will keep them safe from terrorist missiles that are being aimed at the city.
The instructions issued by the Home Front Command are generally issued at the start of a serious clash with Gaza terrorists.
"I have decided not to take a risk on our children's lives and to cancel education in all educational settings in Ashkelon."