Mumbai, Oct 11 (IANS): Choreographer-filmmaker Farah Khan is floored by the energy and passion that megastar Amitabh Bachchan exhibits at the age of 71.

Farah got to choreograph the legend, who celebrates his 71st birthday Friday, in the songs "Say Shava Shava" and "Rock n Roll".

"He (Amitabh Bachchan) is a phenomenal actor and the amount of hard work he does even now is amazing. I know this as I have choreographed songs with him," Farah told reporters Thursday at the premiere of the film "Baat Bann Gayi".

"I have done songs like 'Shava Shava', 'Rock n Roll' with him. He is just amazing. The amount of energy, hard work and passion he still has is just unparalleled," she added.

Recalling the time when she was shooting with Big B, Farah said he works tirelessly.

"He was the most hard working actor. He used to do rehearsals and I never saw him leaving the work in between and going into the vanity van," she said.

"Either he used to sit there on the set reading a book or kept on asking me for the rehearsal. We used to get tired, but he never used to get tired," recalled the filmmaker.

She is herself a big fan of the megastar known for giving hits like "Zanjeer" and "Sholay".

"Every Friday Sajid (Khan) and I used to go to Chandan and Lido cinemas to watch his movies. That used to be an outing for us," she said.