The Israeli military has announced "war footing" after a barrage of rockets were fired from Gaza into Israel on Saturday morning.

A woman in her 60s was killed "due to a direct hit" and 15 others were injured in southern Israel, the Magen David Adom emergency medical services said, after dozens of rockets were fired from the blockaded enclave. The Times of Israel reported that at least five people are thought to have been killed and at least 100 people have been injured.

"The Hamas will bear consequences of the attack on Israel," said the Israeli military.

Mohammed al-Deif, a leader from Hamas, announced on Saturday the beginning of a new military operation, the "Al-Aqsa Flood," against Israel. He made the declaration through a brief recorded statement.

Sirens are sounding in central Israel, the Israel Defense Forces (IDF) said in a statement. 

The Israeli army warned of sirens across the country's south for more than an hour, urging the public to stay near bomb shelters.

Hours later, the IDF said on social media that it carried out strikes on Hamas targets in the Gaza Strip "in response to the barrages of rockets launched by Hamas from Gaza at Israel."

(With input from agencies)