A massive explosion and fire rocked a port in southern Iran on Saturday, killing at least four people and injuring more than 500 others, state television reported.

The blast happened at the Shahid Rajaei port just outside Bandar Abbas, a major facility for container shipments for the Islamic Republic that handles some 72 million tonnes of goods a year.

Social media videos showed black, billowing smoke after the blast. Others showed glass blown out of buildings kilometres away from the epicentre of the explosion.

State media footage showed the injured crowding into at least one hospital, with ambulances arriving as medics rushed one person by on a stretcher.

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 Shahid 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.

The Interior Ministry also said it launched an investigation into the incident.

Shahid Rajaei port in Hormozgan province is some 1,050 kilometres southeast of Iran's capital, Tehran, on the Strait of Hormuz, the narrow mouth of the Persian Gulf through which 20 per cent of all oil traded passes.

In 2020, a suspected Israeli cyberattack targeted the port. It came after Israel said it thwarted a cyberattack targeting its water infrastructure, which it attributed to Iran.

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.