Iran's most expensive ever movie, "Muhammad", which chronicles the childhood of the Muslim prophet, opened nationwide on Thursday, winning praise from early audiences.

Directed by Majid Majidi, the 171-minute, visually stunning film cost around $40 million (35.7 million euros), partly funded by the state, and took more than seven years to complete.

Majidi has said the aim of his work, the first part of a trilogy, is to reclaim the rightful image of Islam, which he said extremists have wrongly made violent.

"Muhammad," which captures Saudi Arabia more than 1,400 years ago, offers much more than stereotypical trains of Arabs on camels riding across yellow sand dunes.

It takes us from the miraculous birth of the future prophet up to his teenage years, and is packed with miracles.

In one scene, an army of tribesmen mounted on elephants charges the holy city of Mecca to heart-pounding music, only to be destroyed by a flock of crows hurling stones.

In another, intensely emotional scene, the boy heals his nanny with a touch of his hand.

"It was very moving for us," said Mahsa Rasoulzadeh, 40, accompanied by her mother and teenage daughter at Kourosh Cinema in west Tehran.

- Strong demand in Tehran -

 The theatre was around two-thirds full at an 11:00 am showing on Thursday, the first day of the Iranian weekend, but afternoon sessions were sold out in advance and two more had to be added for after midnight to meet demand.

Abolfazl Fatehi, 21, who came to watch the film in a family group of seven, said he loved it.

"I think this film can be a starting point of research for those who don't know Islam," he said.

Mehdi Azar, a 25-year-old worker at the cinema, said "it's a long movie and that might seem a turn-off at first, but it's attractive enough to draw an audience. It was very attractive visually."

The crew of "Muhammad" included three-time Oscar-winning Italian cinematographer Vittorio Storaro, with the score devised by India's Allah Rakha Rahman, a double Academy Award winner for the Danny Boyle-directed blockbuster "Slumdog Millionaire."

The film is the second major production on the prophet.

The first, "Muhammad, Messenger of God", was made in 1976 by Syrian-American filmmaker Moustapha Akkad.

It was a huge success with Shiite Iranians.

Forty years on, with its cost around 20 times higher than any other Iran-produced film, Majidi's effort has raised high expectations, not all of which have been met.

"I had heard so much about it...  but, to be honest, my expectations were much higher than what I saw," said Komeil Arjmandi, 23, who is studying film direction.

"I wanted the film to rise higher than Mr Akkad's movie."

Yet, officials don't want the film to be compared with others.

In order to "preserve the dignity" of the prophet, "Muhammad" was excluded from competition in Iran's major Fajr festival in February and was instead showcased in a separate showing.

While Iran has denounced cartoons of the prophet like those published by French satirical magazine Charlie Hebdo, Shiites are generally more relaxed than Sunnis about depiction of religious figures.

Many showings of "Muhammad" in Shiite-majority Iran have already sold out, but the film has triggered controversy in the Sunni world.

Majidi and his cast are in Canada to attend the Montreal Film Festival, which opens Thursday with a screening of "Muhammad."