TEHRAN: A gas tank explosion rocked Tehran overnight near a military complex that had come under scrutiny five years ago from the UN nuclear watchdog, Iran's defence ministry said Friday.

The tanks blew up at around midnight, with Fars news agency saying "a number of social media users reported seeing an orange light" in the east of the Iranian capital.

Amateur footage aired on state television showed what appeared to be a massive orange fireball on the horizon in the middle of the night.

It showed what it said was the aftermath of the explosion in daylight, with at least two large cylindrical tanks damaged by fire along with a scorched nearby field.

The gas tanks "exploded in the Parchin public area. Thank God, there were no casualties," said defence ministry spokesman Brigadier General Davoud Abdi.

"The incident took place in the southeast of Tehran due to leaking gas tanks which occurred in the public area of Parchin and caused the explosion."

The blaze was brought under control by firefighters, and investigations were under way to determine the cause, Abdi told state television.

Parchin is a site suspected of having hosted conventional explosion tests applicable to nuclear power, which the Islamic republic denies.

It had come under scrutiny from the UN's International Atomic Energy Agency in 2015.

Iran had refused the IAEA access to the site because of the nature of its work, but the agency's then chief, the late Yukiya Amano, paid a visit there.

Fars, which is close to ultra-conservatives in Iran, said that according to "videos sent by (our) readers, this light was seen for a few seconds".

It cited an "informed source" and said the site of the incident was not related to the military.

"At the entrance of the (nearby) Parchin military zone, there is no movement or traffic of fire and rescue vehicles," the news agency added.

Fars said that the flash of light was caused by "an industrial gas tank explosion" near a facility belonging to the defence ministry.

Mehr news agency said a "terrible sound" was heard.

State television said various institutions were investigating the incident. Fars said police were involved in the investigation.—AFP