Seven ships were on fire in the Iranian port city of Bushehr, the semi-official Tasnim news agency said on Wednesday.
No casualties were reported, and Tasnim did not say how the incident started.
Fire had broken out at a shipyard, and fire crews were on site, Jahangir Dehghani, the head of the crisis management organisation for Bushehr province, told state-run Irna news agency.
Mr Dehghani said municipal and port firefighters were assisted by crews from the nearby Bushehr Nuclear Power Plant.
Irna said the shipyard builds fibreglass hulls.
Several unexplained explosions and fires have been reported around Iranian military, nuclear and industrial facilities since late June, including a blaze at the underground Natanz nuclear facility in central Isfahan province on July 2.
Natanz is the centrepiece of Iran's enrichment programme, which Tehran said is for peaceful purposes. Western intelligence agencies and the UN's nuclear watchdog (IAEA) believed there was a clandestine nuclear arms programme at the site until 2003. Tehran denies ever seeking nuclear weapons.
Senior Iranian security officials said on July 3 that the cause of the Natanz fire had been determined and would be announced at a later date.
Some officials have said the fire may have been a result of cyber sabotage, and one said that Tehran would retaliate against any country responsible for such attacks.
This month, Irna addressed what it called the possibility of sabotage by enemies such as Israel and the United States, although it stopped short of accusing either directly.
On July 5, Israeli Defence Minister Benny Gantz said his country was not "necessarily" behind every unexplained incident in Iran.
On June 30, 19 people were killed in an explosion at a medical clinic in the north of the capital which an official said was caused by a gas leak.
On June 26, an explosion occurred near the Parchin military and weapons development base about 30 kilometres southeast of Tehran.
The authorities said that was caused by a leak in a gas storage facility outside the base.