UPDATED (5.15 p.m.) - A massive explosion and fire rocked a port Saturday in southern Iran, injuring at least 516 people, state television reported.

The blast happened at the Shahid Rajaei port just outside of Bandar Abbas, a major facility for container shipments for the Islamic Republic that handles some 80 million tons (72.5 million metric tons) of goods a year.

Social media videos showed black billowing smoke after the blast. Others showed glass blown out of buildings kilometers (miles) away from the epicenter of the explosion.

Authorities offered no cause for the explosion hours later, though videos suggested whatever ignited at the port was highly combustible.

Industrial accidents happen in Iran, particularly at its aging oil facilities that struggle for access to parts under international sanctions. But Iranian state TV specifically ruled out any energy infrastructure as causing or being damaged in the blast.

Mehrdad Hasanzadeh, a provincial disaster management official, told Iranian state TV that first responders were trying to reach the area while others were attempting to evacuate the site.

Hasanzadeh said the blast came from containers at Rajaei port in the city, without elaborating. State TV also reported there had been a building collapse caused by the explosion, though there were no immediate other details offered.

Rajaei port is some 1,050 kilometers (650 miles) southeast of Iran’s capital, Tehran, on the Strait of Hormuz, the narrow mouth of the Persian Gulf through which 20% of all oil traded passes.

The blast happened as Iran and the United States met Saturday in Oman for the third round of negotiations over Tehran’s rapidly advancing nuclear program.

Earlier, it was reported that more than 280 people have been injured in a massive blast at a key port in southern Iran on Saturday.

State television, citing local emergency services, reported that “281 people have been injured, dozens of whom have been transferred to medical centres” in the area of the southern port of Shahid Rajaee.

Several containers exploded at a key Iranian port, authorities said, causing a major blast and fire, and leaving several people injured.

State media reported a “massive explosion” at Shahid Rajaee, the country’s largest commercial port located in Hormozgan province on Iran’s southern coast.

“The explosion occurred in a part of the Shahid Rajaee port dock, and we are extinguishing the fire,” state TV quoted Esmaeil Malekizadeh, a regional port official, as saying.

Shahid Rajaee, more than 1,000 kilometres (620 miles) south of the capital Tehran, is the most advanced container port in Iran, according to the official IRNA news agency.

It is located 23 kilometres west of Bandar Abbas, the Hormozgan provincial capital, and north of the Strait of Hormuz through which a fifth of world’s oil output passes.

Footage on state TV showed thick columns of black smoke billowing from the port area where many containers are located.

“Four rapid response teams were dispatched to the scene after the explosion,” Head of the Hormozgan Red Crescent Society, Mokhtar Salahshour, told state TV.

Mehrdad Hassanzadeh, head of the province’s crisis management authority, told state TV that “the cause of this incident was the explosion of several containers stored in the Shahid Rajaee Port wharf area.”

“We are currently evacuating and transporting the injured to nearby medical centres,” he added, without specifying the number of casualties.

--Agencies