MUMBAI: The director of a new Bollywood movie on the 2008 Mumbai attacks is promising an unflinching depiction of the tragedy, which some traumatised survivors fear will be too painful to watch.

“The Attacks of 26/11”, which opens throughout India on Friday, reconstructs the terrifying assault by 10 heavily-armed Islamist gunmen on November 26, 2008 - the start of a 60-hour siege that left 166 people dead.

Director Ram Gopal Varma, a Bollywood veteran known for his gangster and horror films, said he wanted to convey the “emotional aspect” of the deadliest militant attack in India since independence.

“Pretty much everyone knows what happened but they don't know how it happened,” he told AFP.

“The film is very dark and violent. There's no entertainment.”The making of the film has provoked mixed reactions in Mumbai, where feelings still run high over the attacks that targeted luxury hotels, a hospital and a cafe, a busy train station and a Jewish centre.

Some expressed reluctance to drag up memories of the siege and others questioned Varma's ability to pull off such a movie, given his recent run of slated films.

But acting superstar Amitabh Bachchan, who watched a rough cut of the project, wrote on Twitter that it left him “choked with tears” and was “infinitely precise” in its research.

A low-budget film about the attacks was released in 2010 but was panned by critics and soon disappeared.

The seven-minute opening of Varma's film, which includes the gunmen hijacking a fishing boat to reach Mumbai's shores, was released on YouTube in November and has notched up more than one million views.

The budget for the project was initially reported at 400 million rupees ($7.4m), although Varma declined to confirm the final cost.

He said the film was “absolutely based on the true incidents”, showing the trauma people went through and how the attackers appeared -- especially Mohammed Ajmal Kasab, the only gunman to survive the siege.

“Everyone knows Kasab shot down a lot of people but what was his expression like?” said Varma.

Pakistani-born Kasab was hanged in November, aged 25, after his conviction for a string of offences including waging war against India, murder and terrorist acts.

Varma said he had not purposefully waited for the execution to conclude the film, but that it offered a “perfect ending”.

Kasab and most other characters are played by little-known actors rather than stars of the typically more escapist Bollywood fare, in Varma's quest for a “heightened sense of realism”.

He said he largely based the film on information from the police and other eye-witnesses. Among them was Natwarlal Rotwan, a dry-fruit seller who saw his young daughter shot in the leg in the attack at Mumbai's CST station.

He was invited to the studio to give his views on parts of the movie, but found them hard to watch.

“There is only pain for those who got injured or lost loved ones in such attacks,” Rotwan said.

His daughter Devika, who was just nine when she was shot during the attacks, is another survivor who fears the movie will stir painful memories.

“It is good if a movie is made on the Mumbai attacks as people should know what happened,” said Devika, who is now 14.

“But it is bad for people like me, who are trying to forget things and lead a normal life.”The director sparked controversy just days after the attacks took place, when he was seen touring burned out sections of the landmark Taj Mahal Palace hotel with a local politician and his actor son.

Varma has repeatedly denied allegations that he was already conducting a recce for a possible film and he now refuses to discuss the matter, saying he has “answered that question a million times”.

He also raised eyebrows by holding the launch of the film's songs at the popular Leopold Cafe in south Mumbai, which came under attack by the gunmen.

Varma said the launch was intended in the spirit of the cafe owner, who refused to be cowed and reopened just two days after the attacks. But others found the director's choice of venue tasteless.

“It's a just a gimmick to get eyeballs, to get people to talk about it,”said Indu Mirani, a freelance entertainment reporter in Mumbai. “He used to be a sensitive man but he seems to have lost it along the way.”

Farzad Jehani, the cafe's owner, played himself in the movie and defended Varma's project.

He said he was initially “a bit scared” to take on the role, “but then soon I got to terms with that and he has made a fabulous film”.