0600 GMT January 19, 2020
Governor Gholamreza Shariati said he ordered the evacuation of five districts as a "precautionary and preventive move to avert any danger."
The districts have an estimated population of between 60,000 and 70,000.
Shariati asked young men to "help us in building dykes and to assist in the evacuation of women, children and the elderly."
Rivers join each other
"The Dez and Karkheh rivers have for the first time joined each other near Ahvaz and flowed toward the city," Shariati told state TV, adding this was unprecedented.
"The two rivers are far away from each other, but the huge volume of floodwater caused them to join up."
Shariati said a sixth district was also put on standby for possible evacuation.
Khuzestan Province has been struggling with major floods due to heavy rains as well as floodwater coming from the north.
It is the latest in a series of unprecedented floods that have hit the normally arid country since March 19, killing at least 70 people.
The country's northeast was first swamped on March 19 before the west and southwest of the country were hit on March 25.
On April 1, the west and southwest were again swamped by floods when heavy rains returned to the area.
Floods described by officials as the worst since the 1940s have hit some 1,900 cities and villages across Iran after exceptionally heavy rain since March 19. Western and southwestern areas of the country are suffering the worst.
The disaster has left aid agencies struggling to cope, and the Armed Forces were deployed to help flood-hit people.
The government has told citizens, and especially flood-affected farmers, that all losses will be compensated.
Officials have repeatedly said the massive floods have not affected production and development of oilfields, or the flow of crude through pipelines to recipient markets.
Following the devastating floods, many countries, neighbors in particular, rushed to help the affected people by sending humanitarian aid.
On Wednesday, Pakistan dispatched first batch of humanitarian aid to Iran, Iran’s Ambassador to Pakistan Mehdi Honardoost told IRNA.
He said that a C-130 aircraft carrying relief goods flew to Iran on Wednesday while another aircraft leaves today.
He said that the National Disaster Management Authority (NDMA) of Pakistan sent over 32 tons of humanitarian assistance containing 500 tents, 2,500 blankets and emergency medical kits.
Also on Wednesday, Oman sent relief flights to Iran, according to Oman TV’s official Twitter account.
Azerbaijan’s Deputy Emergency Situations Minister Faig Taghizadeh told reporters in Baku on Wednesday that Azerbaijan has sent aid supplies for Iranians.
“The humanitarian aid, worth some $600,000, has been sent to Iran at the order of Azerbaijani President Ilham Aliyev,” Taghizadeh said.
Several regional countries, such as Turkey, Russia and Kuwait as well as some European countries have sent in in-kind assistance to Iran.
Reuters and AFP contributed to this story.