Israeli Prime Minister Benjamin Netanyahu vowed to defeat Hamas following the group's surprise attacks, but told his nation that the war "will take time."
In a televised speech, Netanyahu said what happened "has never been seen in Israel" and vowed to take "mighty vengeance for this black day."
He vowed that Israel would reach every place that Hamas is hiding in.
"I tell Gaza's people to leave those places now," the prime minister added.
He also told Hamas that he holds the militant group personally responsible for the safety and wellbeing of Israeli civilians and soldiers it has taken captive, adding that Israel will "settle the score with anyone who harms them."
How did Hamas' attacks unfold on Saturday and how did Israel respond?
The Palestinian militant group Hamas launched a surprise attack on Israel from the Gaza Strip on Saturday.
Hamas is classified by the European Union and the United States as a terrorist organization.
The attack came on the 50th anniversary of the Yom Kippur war, in which Syria and Egypt launched a surprise offensive on Israel.
Gun battles raged between Israeli forces and hundreds of Hamas fighters in at least 22 locations, Israel's army said.
Israeli rescue service Zaka reported that 300 people were killed in Israel during the attacks and 1,590 were wounded as of Saturday evening. Israel's army said that over 200 Israelis were killed and 1,000 wounded.
The Israeli army confirmed that several Israeli citizens, some of them soldiers, had been taken hostage in the fighting and were being held in the Gaza Strip, without giving an exact number. A Hamas spokesman later claimed that "dozens of soldiers" were being held in Gaza.
The Gaza Health Ministry said that 242 people have been killed and some 1,700 wounded in strikes by the Israeli army after Hamas launched its attacks.
Rocket alerts sounded in the greater Tel Aviv area and other Israeli cities on Saturday evening.
The Magen David Adom rescue service said that several people were injured in the attacks, three of them seriously.
Israeli media cited the fire brigade as saying that a building in Tel Aviv had been hit by rockets and collapsed.
Hamas said that it had fired another 150 rockets at Israel in retaliation for strikes that hit a building in Gaza. Israel's army said it attacked the building because it had been used by senior Hamas members for terrorist activities.
Berlin's Brandenburg Gate lit up in colors of Israeli flag
Late on Saturday, Berlin's Brandenburg Gate lit up with the colors of the Israeli flag following a deadly attack by Hamas fighters.
Meanwhile, Germany moved to reinforce security around Jewish temples, schools and monuments after the attack.
"In Berlin, police protection has been immediately stepped up," Germany's Interior Minister Nancy Faeser told the Bild newspaper. "The federal government and the regions are closely coordinating their actions."
She said that German authorities were closely watching "potential supporters of Hamas in the Islamist sphere."
Hamas is classified by Germany, the EU and the US as a terrorist organization.
Berlin police posted photos on social media showing "people celebrating the attacks on Israel by passing out pastries" on the major street of Sonnenallee in the Neukölln district. In some cases, officers carried out identity checks and filed complaints, police said.
Neukölln District Mayor Martin Hikel described the event as "a horrible glorification of a terrible war," calling for a ban on "disgusting terrorist propaganda."
Blinken speaks with regional power Egypt to de-escalate crisis
US Secretary of State Antony Blinken said he met with Egyptian Foreign Minister Sameh Shoukry to discuss Hamas' surprise attack.
"I spoke with Egyptian Foreign Minister Sameh Shoukry about the horrific attacks by Hamas terrorists against Israel," he said. "We appreciate Egypt’s ongoing efforts and reiterate the urgent need to halt the Hamas attacks."
Egypt, which borders the Gaza Strip, has mediated previous cease-fires between Israel and Palestinian militants. In June, Egypt helped broker a truce between Israel and the Islamic Jihad militant group.
Blinken also spoke with Saudi Arabia's Foreign Minister Prince Faisal bin Farhan regarding the attacks on Israel. The two sides "called for coordinated efforts to achieve an immediate halt to the Hamas terrorists and other militants," according to a US State Department press release.
The Hamas attack on Israeli territory comes as the US attempts to broker a deal that would normalize ties between Saudi Arabia and Israel.
At least 80 passenger flights to Tel Aviv canceled
Airlines have canceled more than 80 flights to and from Tel Aviv following Hamas' incursion in Israeli territory.
This amounts to roughly 14% of all flights scheduled for Saturday evening.
German carrier Lufthansa canceled several flights between Frankfurt and Tel Aviv.
American Airlines, Air France, Emirates, Ryanair, Italy's ITA, Spain's Iberia Express, Poland's LOT and Greece's Aegean Airlines also pulled flights.
However, airport authorities did not stop commercial air links with Israel's second-largest international airport, located near the Red Sea city of Eilat.
Meanwhile, the US' air regulator, the Federal Aviation Administration (FAA), urged airlines and pilots to use caution when flying in Israeli airspace.
The Israeli government previously issued a similar warning.
China calls for restraint, cease-fire
China said that it was "deeply concerned" at the developments in Israel and the Palestinian territories.
"China is deeply concerned about the current escalation of tension and violence between Palestine and Israel," the Chinese Foreign Ministry said.
The ministry said it "calls on all parties concerned to remain calm and exercise restraint, cease fire immediately, protect civilians and prevent further deterioration of the situation."