More than 500 people were injured Saturday as a large explosion ripped through a key port in southern Iran, state media said, with the cause of the blast not immediately clear.

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 Tansnim news agency said at least 516 people had been wounded. There was no immediate information on possible fatalities.

Citing local emergency services, state television reported that many “people have been injured, dozens of whom have been transferred to nearby medical centers,” revising earlier tolls.

“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.

Efforts were ongoing to extinguish a significant fire, with the port’s customs saying that trucks were being evacuated from the area and that the container yard where the explosion occurred likely contained “dangerous goods and chemicals.”

State TV said “negligence in handling flammable materials was a contributing factor” in the explosion.

Shahid Rajaee, more than 1,000 kilometers (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 kilometers west of Bandar Abbas, the Hormozgan provincial capital, and north of the Strait of Hormuz through which a fifth of the 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.

As emergency services dispatched rapid response teams to the port, First Vice President Mohammad Reza Aref ordered an investigation to determine the cause of the blast and assess the extent of the damage, according to the ISNA news agency.

Mehrdad Hassanzadeh, head of Hormozgan 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 centers,” he said.

The explosion was so powerful that it could be felt and heard some 50 kilometers away, Fars news agency reported, with residents saying they could feel the ground shake even at a distance from the port.

“The shockwave was so strong that most of the port buildings were severely damaged,” Tasnim news agency reported.

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 have offered no cause for the explosion yet. 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.

The state-owned National Iranian Oil Products Distribution Company said in a statement carried by local media that “the explosion at Shahid Rajaee Port has no connection to refineries, fuel tanks, distribution complexes or oil pipelines.”

It added that “Bandar Abbas oil facilities are currently operating without interruption.”

The rare explosion comes several months after one of Iran’s deadliest work accidents in years.

A coal mine blast in September caused by a gas leak killed more than 50 people in Tabas, in Iran’s east, prompting authorities to announce public mourning.

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.

In 2020, computers at the same port were hit by a cyberattack that caused massive backups on waterways and roads leading to the facility. The Washington Post had reported that Iran’s arch-foe, Israel, appeared to be behind that incident as retaliation for an earlier Iranian cyberattack.

There was no immediate comment from the Israeli military or Prime Minister Benjamin Netanyahu’s office when asked for comment on whether Israel was in any way involved in the explosion.