At least nine people killed, thousands injured after Hezbollah pagers ...

At least nine people have been killed and about 2,800 others injured after pagers used by the militant group Hezbollah exploded in a wave of blasts across Lebanon. 

The country's health ministry said an eight-year-old girl was among the dead.

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A Hezbollah official, speaking on condition of anonymity to Reuters, said the detonation of the pagers was the "biggest security breach" the group had been subjected to in nearly a year of conflict and tensions with Israel.

Experts said the pager explosions pointed to a long-planned operation, possibly carried out by infiltrating the supply chain and rigging the devices with explosives before they were delivered to Lebanon.

The Iranian-backed militant group blamed Israel for the widespread attack and said it would get "its fair punishment".

The Israeli military declined to comment. 

At about 3:30 pm local time, as people shopped for groceries, sat in cafes or drove through the afternoon traffic, the pagers in their hands or pockets started heating up and then exploding — leaving blood-splattered scenes and panicking bystanders.

A witness has told ABC News of seeing one of the pagers exploding on a man riding a motorcycle in the Lebanese capital, Beirut.

Ambulances have been seen rushing to hospitals across Beirut.   (Reuters: Mohamed Azakir)

Other witnesses have reported ambulances rushing through the southern suburbs of Beirut amid widespread panic.

The blasts were mainly in areas where the Hezbollah group has a strong presence, particularly a southern Beirut suburb and in the Beqaa region of eastern Lebanon, as well as in Damascus. 

Regional news outlets have broadcast CCTV footage showing what appeared to be a small handheld device spontaneously exploding after being placed next to a grocery store cashier where an individual was paying.

Hezbollah sources said the group's chief, Hassan Nasrallah, was not harmed in the blasts.

Ambulance and hospital staff were mobilised across Lebanon to deal with the number of casualties following the explosions. (Reuters: Mohamed Azakir)

However, Iran's semi-official Fars news agency reported that Iran's ambassador to Lebanon, Mojtaba Amani, was slightly injured by the explosion of an electronic pager.

Three security sources told Reuters news agency the pagers that detonated were the latest model brought in by Hezbollah in recent months.

At overwhelmed hospitals, wounded were rushed in on stretchers, some with serious injuries, according to witnesses. 

Beirut's health ministry called for civilians to donate blood to help those caught up in the attack. 

People registered to donate blood in Lebanon as the number of those wounded in the attack continued to rise. (Reuters: Aziz Taher)

Lebanon's crisis operations centre, which is run by the health ministry, asked all medical workers to head to their respective hospitals to help cope with the massive numbers of wounded coming in for urgent care.

It said healthcare workers should not use pagers.

Hezbollah has placed the blame for the attack square on its sworn enemy, Israel. 

Lebanese soldiers stand guard at a street that leads to the American University hospital in Beirut after the attack.  (AP: Hassan Ammar)

"We hold the Israeli enemy fully responsible for this criminal aggression that also targeted civilians," Hezbollah said in a statement, adding that Israel will "for sure get its just punishment."

The Israeli military, which has been engaged in cross-border fighting with Iran-backed Hezbollah since the start of the Gaza war in October, declined to respond to questions about the detonations.

This year, separate Israeli air strikes in Beirut killed Saleh Arouri, a senior Hamas official, and a top Hezbollah commander. 

A mysterious explosion in Iran, also blamed on Israel, killed Ismail Haniyeh, Hamas' supreme leader.

Israel has killed Hamas militants in the past with booby-trapped mobile phones and it's widely believed to have been behind the Stuxnet computer virus attack on Iran's nuclear program in 2010.

The pager bombings also likely stoke Hezbollah's worries about vulnerabilities in security and communications. 

It's believed the pagers were bought specifically so that Israeli intelligence officials could not listen into the group's conversations over the phone. 

Unlike mobile phones, pagers work on radio waves — the operator can send a message by radio frequency rather than the internet.

The near daily exchanges of fire between Israel and Hezbollah have killed hundreds in Lebanon and several dozen in Israel, and have displaced tens of thousands on both sides of the border.

Jeanine Hennis-Plasschaert, the UN special coordinator for Lebanon, deplored the attack and warned that it marks "an extremely concerning escalation in what is an already unacceptably volatile context". 

ABC/AP/Reuters