Earlier, Iranian state media reported that at least one person had been killed and 14 injured in the blast, which comes amid heightened tensions between Iran and the United States over Iranian government's crackdown earlier this month on protests and over the country's nuclear program.
"This (gas leak and accumulation) is the preliminary assessment. My colleagues will give more details in the next few hours," Mohammad Amin Liaqat, the fire department chief, said in a video published by the Mehr news agency.
The state news agency IRNA published a photo of the partially destroyed front of a multi-storey residential building.
A video published on social media showed people standing among debris and wrecked cars in front of a damaged building following the explosion.
Reuters was able to verify the location by analysing buildings, trees and road layout which matched satellite and file imagery.
Reuters could not independently verify the date the video was filmed.
Separately, four people were killed after another gas explosion in the city of Ahvaz near the Iraqi border, according to the state-run Tehran Times.
No further information was immediately available.
The explosions highlighted the jittery mood prevailing in Iran amid its clerical rulers' stand-off with the administration of US President Donald Trump.
Before the reports of the two blasts on Saturday, Iranian President Masoud Pezeshkian accused US, Israeli and European leaders of exploiting Iran's economic problems, inciting unrest and providing people with the means to "tear the nation apart".
The Tasnim news agency said social media reports alleging that a Revolutionary Guard navy commander had been targeted in the Bandar Abbas explosion were "completely false".
Two Israeli officials told Reuters that Israel was not involved in Saturday's blasts.
Trump said on January 22 an "armada" was heading toward Iran.
Multiple sources said on Friday that Trump was weighing options against Iran that include targeted strikes on security forces.
Bandar Abbas, home to Iran's most important container port, lies on the Strait of Hormuz, a vital waterway between Iran and Oman which handles about a fifth of the world's seaborne oil.
The port suffered a major explosion last April that killed dozens and injured more than 1000 people.
An investigative committee at the time blamed the blast on shortcomings in adherence to principles of civil defence and security.
Iran has been rocked by protests that erupted in December over economic hardship and have posed one of the toughest challenges to the country's clerical rulers.
with DPA
