A massive explosion tore through Iran's largest commercial port on Saturday, triggering a major blaze, with 14 people killed and 750 injured so far.

The blast occurred at Shahid Rajaee Port in southern Iran, near the Strait of Hormuz through which a fifth of world oil output passes.

Although the cause of the blast was not immediately clear, the port's customs office said in a statement carried by state TV that it probably resulted from a fire that broke out at the hazardous and chemical materials storage depot.

The New York Times reported that a person with ties to Iran's Islamic Revolutionary Guard Corps, speaking on condition of anonymity to discuss security matters, told the newspaper that what exploded was sodium perchlorate, a major ingredient in solid fuel for missiles.

Interior Minister Eskandar Momeni said on Telegram early Sunday that there were "14 dead and 750 injured so far in the explosion."

With choking smoke spreading throughout the area, all schools and offices 23 kilometers (14 miles) away in Bandar Abbas, the capital of Hormozgan province, have been ordered closed on Sunday, state TV said, to allow authorities to focus on the emergency effort.

"The intensity of the fire in Shahid Rajaee Port has increased and it is possible that the fire could spread to other areas and containers," state TV said late Saturday.

Strong winds were complicating efforts to extinguish the flames, a reporter for the broadcaster said.

Shahid Rajaee, more than 1,000 kilometers south of Tehran, is Iran's most advanced container port, according to the official IRNA news agency.

Images from IRNA showed rescuers and survivors walking along a wide boulevard carpeted with debris after the blast.

Flames engulfed a truck trailer and blood stained the side of a crushed car, while a helicopter dropped water on massive black smoke clouds billowing from behind stacked shipping containers.

Citing local emergency services, state TV reported that "hundreds have been transferred to nearby medical centers," while the provincial blood transfusion center issued a call for donations.

Iranian President Masoud Pezeshkian expressed sympathy for the victims of the deadly blast, adding he had "issued an order to investigate the situation and the causes."

He said Momeni would go to the area to look into the incident.

Speaking later at the scene, Momeni told state TV: "All resources from other cities and Tehran have been dispatched... and we hope to be able to extinguish the fire in the coming hours."

In a video posted to social media, which AFP was not able to verify, a man filming the disaster said "my truck was completely destroyed and my friend died." A dead body can be seen on the ground.

Containers exploded

Saturday is the start of the working week in Iran, meaning the port would have been busy with employees.

Three Chinese nationals were "lightly injured," China's state broadcaster CCTV reported, citing its Bandar Abbas consulate.

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."

The explosion was so powerful that it was felt and heard about 50 kilometres away, Fars news agency reported.

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

The United Arab Emirates expressed "solidarity with Iran" over the explosion and Saudi Arabia sent condolences.

The state-owned National Iranian Oil Products Distribution Company said in a statement carried by local media that the explosion "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 explosion comes several months after one of Iran's deadliest work accidents in years.

The coal mine blast in September, caused by a gas leak, killed more than 50 people at Tabas in the east of the country.

Saturday's explosion also came as Iranian and US delegations met in Oman for high-level talks on Tehran's nuclear programme. Both sides reported progress, with a US official calling it "positive and productive."