A massive explosion that tore through Beirut left some 300,000 people homeless, and Lebanese port officials have been placed on house arrest Wednesday amid an investigation into what caused the blast that so far has killed at least 135 people and injured thousands more.

Beirut’s Gov. Marwan Abboud said Wednesday that some 300,000 people might not be able to return to their homes for two to three months as the rescue crews continue to sift through collapsed buildings and rubble for survivors, UK’s The Telegraph reported.

International aid flights have begun to arrive as hospitals in the country already suffering from a severe economic crisis are overwhelmed with the wounded. One hospital damaged by the blast had to evacuate patients to a field for treatment. Abboud said he expects the death toll to continue to rise as hundreds of people have been reported missing.

BEIRUT EXPLOSION: RESCUE WORKERS FRANTICALLY SEARCH FOR SURVIVORS AS LEBANON CAPITAL CONFRONTS MASSIVE DEVASTATION

Lebanon’s President Michel Aoun vowed before a cabinet meeting on Wednesday that the investigation would be transparent and that those responsible will be punished.

“There are no words to describe the catastrophe that hit Beirut last night,” he said.

Lebanese soldiers search for survivors after a massive explosion in Beirut, Lebanon, Wednesday, Aug. 5, 2020. (AP Photo/Hassan Ammar)

Lebanese soldiers search for survivors after a massive explosion in Beirut, Lebanon, Wednesday, Aug. 5, 2020. (AP Photo/Hassan Ammar)

The cabinet ordered an unspecified number of Beirut port officials put under house arrest pending an investigation into how ammonium nitrate came to be stored at the port for years. The government also declared a two-week state of emergency, effectively giving the military full powers during this time.

An official letter has surfaced online showing that the head of the customs department had warned repeatedly over the years that a huge stockpile of ammonium nitrate stored in a hangar in the port was a danger and asked for a way to remove it.

Ammonium nitrate is a component of fertilizer that is potentially explosive. The 2,750-ton cargo had been stored at the port since it was confiscated from a ship in 2013, and on Tuesday it is believed to have detonated after a fire broke out nearby. The cause of the fire remains unclear.

BEIRUT BLAST DEVASTATION SEEN IN NEW SATELLITE IMAGES 

A general view of the scene of an explosion that hit the seaport of Beirut, Lebanon, Wednesday, Aug. 5, 2020. (AP Photo/Bilal Hussein)

A general view of the scene of an explosion that hit the seaport of Beirut, Lebanon, Wednesday, Aug. 5, 2020. (AP Photo/Bilal Hussein)

The resulting explosion — hitting with the force of a 3.5-magnitude earthquake — was the biggest ever seen in Beirut, a city blasted by a civil war between 1975-1990, bombarded in conflicts with Israel and hit by periodic terror attacks.

State prosecutor Ghassan Oueidat ordered security agencies to start an immediate investigation and collect all reports and letters related to the materials stored at the port as well as lists of people in charge of maintenance, storage and protection of the hangar. If authentic, the letter could deepen the belief already expressed by some Lebanese that widespread mismanagement, negligence and corruption among the country’s ruling class is to blame for the explosion.

Several sources in the region told Fox News that the port has been unofficially controlled by Hezbollah – though it remains too early to call whether the explosion was an intentional act of terrorism or an accidental result of a lack of checks on organized crime.

In the letter, the customs chief warns of the “dangers if the materials remain where they are regarding the safety of [port] employees” and asked the judge for guidance on what to do with it. He said five similar letters were sent in 2014, 2015 and 2016. The letter proposes the material be exported or sold to a Lebanese explosives company. It is not known if there was ever a response.

A drone picture shows the scene of an explosion at the seaport of Beirut, Lebanon, Wednesday, Aug. 5, 2020. (AP Photo/Hussein Malla)

A drone picture shows the scene of an explosion at the seaport of Beirut, Lebanon, Wednesday, Aug. 5, 2020. (AP Photo/Hussein Malla)

The government said public schools will be opened to host those who lost their homes and the minister of tourism will also work on opening some hotels for use by those rendered homeless by the explosion. It also promised compensation for the victims.

With the Port of Beirut destroyed, the government said imports and exports will be secured through other ports in the country, mostly in the northern city of Tripoli and the southern port city of Tyre.

Smoke was still rising from the port early Wednesday where a towering building of silos was half destroyed, spilling out grain. Hangars around it were completely toppled. The blast knocked out a crater some 650 feet across that filled with seawater. Much of downtown was littered with damaged vehicles and debris that had rained down from the shattered facades of buildings.

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French President Emmanuel Macron is expected to travel to Beirut on Thursday to offer support and meet with Lebanese leaders. Lebanon is a former French protectorate and the countries retain close political and economic ties.

Fox News’ Lucas Tomlinson, Hollie McKay and The Associated Press contributed to this report.