Thor: Ragnarok opens strongly with $121M US at box office

Thor: Ragnarokthundered to one of the year's best box-office debuts, opening with an estimated $121 million US in North American theatres.

The robust debut for the third Thormovie was a welcome shot in the arm for Hollywood and theatreowners who have just suffered through a terrible October at the box office.

Thor: Ragnarokalso bucked the trend of diminishing returns for sequels. The 2011 Thordebuted with $65.7 million; 2013's Thor: The Dark Worldopened with $85.7 million.

The big opening cements the unlikely breakthrough of New Zealand director Taika Waititi, who shepherded the $180 million production to Marvel's best reviews since 2008's Iron Man.

The weekend's other new nationwide release was the holiday-themed comedy sequel A Bad Mom's Christmas.It grossed $17 million over the weekend.