A 13-storey residential block in the Gaza Strip collapsed on Tuesday night after being hit by an Israeli airstrike, witnesses said, and three people were wounded in a retaliatory rocket attack from Gaza on Tel Aviv.
Video footage showed three plumes of thick, black smoke rising from the Gaza tower, its upper storeys still intact as they fell. The building houses an office used by the political leadership of the enclave's Islamist rulers, Hamas.
Electricity in the surrounding area went out, and residents were using flashlights.
Shortly after the attack, Hamas and the Islamic Jihad group said they would respond by firing rockets at Tel Aviv.
Air raid sirens and explosions were heard around the city, and the skies were lit up by the streaks of multiple interceptor missiles launched towards the incoming rockets.
Pedestrians ran for shelter, and diners streamed out of Tel Aviv restaurants while others flattened themselves on pavements as the sirens sounded. Israeli television stations said three people had been wounded in the suburb of Holon.
The Israel Airports Authority said it had halted take-offs at Tel Aviv's Ben Gurion airport "to allow defence of (the) nation's skies".
The U.S. State Department urged restraint on both sides.
"We are now carrying out our promise," Hamas's armed wing said in a statement. "The Qassam Brigades are launching their biggest rocket strike against Tel Aviv and its suburbs, with 130 rockets, in response to the enemy’s targeting of residential towers."
Hours earlier, Israel had sent 80 jets to bomb Gaza and massed tanks on the border as rocket barrages hit Israeli towns for a second day, deepening a conflict in which at least 28 people in the Palestinian enclave and two in Israel have been killed.
Residents of the block and people living nearby had been warned to evacuate the area around an hour before the air strike, according to witnesses, and there were no reports of casualties two hours after it collapsed.
The most serious outbreak of fighting since 2019 between Israel and armed factions in Gaza was triggered by clashes between Palestinians and Israeli police at Jerusalem's al-Aqsa Mosque on Monday.
The city, holy to Jews, Muslims and Christians, has been tense during the Muslim fasting month of Ramadan, with the threat of a court ruling evicting Palestinians from homes claimed by Jewish settlers adding to the friction.
Prime Minister Benjamin Netanyahu said Israel would step up its strikes on Gaza, an enclave of 2 million people, in response to the rocket attacks.
"Both the strength of the attacks and the frequency of the attacks will be increased," he said in a video statement.
Within an hour, Israel said it had deployed jets to bomb rocket launch sites in and around Gaza City.
Officials said infantry and armour were being dispatched to reinforce the tanks already gathered on the border, evoking memories of the last Israeli ground incursion into Gaza to stop rocket attacks, in 2014.
More than 2,100 Gazans were killed in the seven-week war that followed, according to the Gaza health ministry, along with 73 Israelis, and thousands of homes in Gaza were razed.
On Tuesday, before the block collapsed, the Gaza health ministry said at least 28 Palestinians, including 10 children, had been killed and 152 wounded by Israeli strikes since Hamas on Monday fired rockets towards Jerusalem for the first time since 2014.
Israel's national ambulance service said two women had been killed in rocket strikes on the southern city of Ashkelon.
The International Committee of the Red Cross urged all sides to step back and reminded them of the requirement in international law to try to avoid civilian casualties.