At least seven boats have caught fire at a shipyard in the southern port of Bushehr, state media report.
The head of the local crisis management organization informed the Irna news agency that the fire had been contained and no victims had been reported.
The cause was not clear, but it is the latest in a series of mysterious incidents in Iran in the past few weeks.
This included explosions and fires in a missile facility, a power plant, a medical clinic and an atomic complex.
The incidents have led to speculation about a sabotage campaign.
- Iran denies reports of a new explosion
- What is behind mysterious fires in Iranian locations?
On Monday there was a fire in an industrial area near the northeast city of Mashhad. Officials said six gas storage tanks caught fire and exploded.
The day before, a fire broke out in a petrochemical plant in southwest Mahshahr due to an oil leak.
And on Saturday, several gas bottles exploded in the basement of a residential building in Tehran, the fire department told the capital.
Iranian officials have said they are investigating whether sabotage by foreign powers or domestic opposition groups may have caused earlier explosions at the Natanz uranium enrichment facility on July 2 and the Khojir missile production facility on June 26.