A huge explosion near the centre of Beirut killed at least 10 people and sent shockwaves across the Lebanese capital, shattering glass in people's homes and causing apartment balconies to collapse, witnesses and security sources said.

The blast occurred in the city's port area, where there were warehouses housing explosives, Lebanon's state news agency NNA and two security sources said. A third security source said there were chemicals stored in the area.

Footage of the blast shared around by residents on social media showed a column of smoke rising from the port district followed by an enormous blast. Those who filming what initially appeared to be a big blaze were thrown backwards by the shock.

At least 10 bodies were taken to hospitals, a security source and a medical source told Reuters.

Hundreds of injured were taken to hospitals but many remain trapped in homes damaged by the explosion, the head of the Lebanese Red Cross said.

George Kettaneh told local media there was no exact figure of how many were injured as many were still trapped in homes and within the area of the blast. Others were being rescued by boat.

Lebanese broadcaster LBCI quoted Hotel Dieu Hospital in Beirut as saying that it was treating more than 500 injured and was not able to receive more. Tens of injured needed operations, the hospital said, appealing for blood donations.

Cause unclear

It was not immediately clear what caused the blaze that set off the blast or what kind of explosives were in the warehouses. The governor of Beirut port told Sky News that a team of firefighters at the scene had “disappeared” after the explosion.

Meanwhile, Lebanon's internal security chief Abbas Ibrahim said the blast occurred in a section housing highly-explosive materials, and not explosives as had been reported earlier by the official state news agency, NNA.

Speaking to reporters in televised remarks, he declined to speculate about the cause of the explosion in Lebanon's capital, saying “we cannot preempt investigations”.

“I saw a fireball and smoke billowing over Beirut. People were screaming and running, bleeding. Balconies were blown off buildings. Glass in high-rise buildings shattered and fell to the street,” said a Reuters witness.

The health minister told Reuters there was a “very high number” of injured. Al Mayadeen TV said hundreds were wounded.

Another Reuters witness said she saw heavy grey smoke near the port area and then heard an explosion and saw flames of fire and black smoke: “All the downtown area windows are smashed and there are wounded people walking around. It is total chaos.”

UN spokesman Farhan Haq told reporters it was not immediately clear what the cause was, and that there was no indication of any injuries to any UN personnel.

"We do not have information about what has happened precisely, what has caused this, whether its accidental or man made act," he said.

The US Pentagon said: “We are aware of the explosion and are concerned for the potential loss of life due to such a massive explosion.”

In Cyprus, an island lying west of Lebanon, residents reported two large bangs in quick succession. One resident of the capital Nicosia said his house shook, rattling shutters.