Israeli TV said the salvo was expected to reach Israel at 02:00 on Sunday (23:00 GMT on Saturday).
Iran's Revolutionary Guards said they had launched missiles as well as drones "at specific targets".
Image: SCREENGRAB
Iran has launched a wave of aerial drones at Israel, appearing to mark a widely anticipated reprisal attack.
Israeli TV said the salvo was expected to reach Israel at 02:00 on Sunday (23:00 GMT on Saturday).
Iran's Revolutionary Guards said they had launched missiles as well as drones "at specific targets".
The Israel Defense Forces (IDF) said they were on high alert and "monitoring all targets". Israel's prime minister convened a meeting of his war cabinet.
In an address to the nation, Israeli Prime Minister Benjamin Netanyahu says the military is “ready for any scenario”.
"Citizens of Israel, in recent years, and especially in recent weeks, Israel has been preparing for a direct attack by Iran,” he says.
“Our defensive systems are deployed; we are ready for any scenario, both defensively and offensively. The State of Israel is strong. The IDF is strong. The public is strong.”
He also thanks allies, including the US and UK, for “standing alongside” Israel
Netanyahu adds: “We have determined a clear principle: Whoever harms us, we will harm them. We will defend ourselves against any threat and will do so level-headedly and with determination.”
He calls on Israeli citizens to follow the “directives” of the IDF Home Front Command, adding: “Together we will stand and with God's help – together we will overcome all of our enemies.
Israel, Lebanon and Iraq have closed their airspaces, and Syria and Jordan have put their air defences on alert.
Iran had vowed to retaliate for an attack on its consulate in Syria on April 1 which killed seven military officers, including a top commander.
It accused Israel of carrying out that attack. Israel neither confirmed nor denied it.
"Iran has launched a direct attack from Iranian soil toward the State of Israel," IDF spokesman Rear Admiral Daniel Hagari said. "We are closely monitoring Iranian killer drones that are en route to Israel, sent by Iran. This is a severe and dangerous escalation."
Shortly before news of Iran's drone launches, Israeli Prime Minister Benjamin Netanyahu said his country's "defensive systems" were deployed.
"We are ready for any scenario, both defensively and offensively. The State of Israel is strong. The IDF is strong. The public is strong.
"We appreciate the US standing alongside Israel, as well as the support of Britain, France and many other countries."
Earlier this week, Israel's defence and foreign ministers warned that if Iran attacked Israel, Israel would strike back inside Iran.
After news of the Iranian attack broke, US National Security Council spokesperson Adrienne Watson said: "President Biden has been clear: our support for Israel's security is ironclad."
"The United States will stand with the people of Israel and support their defence against these threats from Iran."
UK Prime Minister Rishi Sunak condemned Iran's "reckless" attack, vowing that the UK would "continue to stand up for Israel's security and that of all our regional partners".
Iran's Islamic Revolution Guard Corps (IRGC) - the most powerful branch of its armed forces - said it had launched the attack "in retaliation against the Zionist regime's [Israel] repeated crimes, including the attack on the Iranian embassy's consulate in Damascus".