A huge fire broke out Thursday at the Port of Beirut, sending up a thick column of black smoke and raising new panic among traumatized residents after last month's catastrophic blast at the same site killed nearly 200 people.

It was unclear what caused the blaze at the facility, which was decimated by the Aug. 4 explosion when nearly 3,000 tons of ammonium nitrate blew up and sent out a shock wave that caused widespread damage and was felt as far away as the island of Cyprus.

Dark smoke covered the capital on Thursday as army helicopters sprayed water over the orange flames leaping from the ground.

The Lebanese army said the fire started in the port's duty free zone at a warehouse with containers of tires, oil and other flammable materials.

Panicked residents - still struggling to recover from last month's explosion - cracked open windows and called and texted each other to warn them of the new danger. Local TV stations said companies that have offices near the port asked employees to leave the area.

Some hid in bathrooms, while others dropped what they were doing and rushed home.

"We opened all windows and are in the corridor right now," said Dana Awad, a mother of two girls in a Beirut neighborhood, recalling the tremor that preceded the earlier explosion. "I am still feeling the earth shake. Living a flashback."

A video on social media showed port employees running in fear from the fire, a chilling reminder of the dozens of workers and 10 firefighters who were killed in the blast. Lebanese troops closed the major road near the port, rerouting traffic to other areas.

The Aug. 4 explosion killed 191 people, injured about 6,500 and damaged thousands of buildings. The explosion, the single most destructive blast in Lebanon's history, is blamed on government negligence and mismanagement.

There was speculation in Beirut that Thursday's fire could be an attempt to destroy evidence from the explosion. Port director Bassem al-Qaisi told Voice of Lebanon radio the fire started in a warehouse where barrels of cooking oil were placed and later spread nearby to where tires were piled.

"It is too early to now if it is the result of heat or some other mistake," al-Qaissi said adding that the black smoke was from burning tires.

The panic was compounded by the fear that more chemicals could be in the wreckage of the port. Earlier this month, the army said it discovered more than 4 tons of ammonium nitrate in four containers stored near the port that it said were "dealt with."

French and Italian chemical experts working amid the remains of the port identified more than 20 containers of dangerous chemicals. The army later said these containers were moved and stored safely away from the port.

Beirut Gov. Marwan Abboud and authorities urged people to stay away from roads leading to the port to allow firefighters to move quickly.

It was the second fire at the port this week. On Tuesday, a small fire also created some panic, but it was quickly extinguished.

From AP