Hopkins, 53, drowned Sunday in the Waiohine River on New Zealand's North Island, the BBC reported. Two people with him survived after all three were ejected from the raft in a fast-flowing eddy, the report said.
Hopkins won Academy Awards for his work on "The Lord of the Rings: The Two Towers" in 2003 and "King Kong" in 2006. Both were big-screen epics Jackson directed. Hopkins also collaborated with Jackson on the movies "Braindead," "Heavenly Creatures," "The Frighteners," "The Lord of the Rings: The Fellowship of the Ring" and "The Lord of the Rings: The Return of the King."
Hopkins' other film credits included "Blade Runner," "Superman," "Octopussy" and "Transformers."
The New Zealand Herald said a family celebration of Hopkins' life is planned for Thursday.
New Zealand's News One quoted Jackson as saying he and his fellow producers -- Fran Walsh, Philippa Boyens, Caro Cunningham and Zane Weiner -- are "deeply shocked and saddened to learn of the tragic death" of Hopkins.
"I know I can speak for the many actors, directors, production and post-production crew who were lucky enough to work with Mike, in saying that he will be terribly missed," Jackson said.
"Mike was an extraordinarily talented sound designer, editor and supervisor and thoroughly deserving multiple Oscar winner. Under his guidance, New Zealand became recognized as one of the leading hubs of post-production sound in the world."
Jackson went on to call the sound expert "a very genuine, caring and warm-hearted guy with a great sense of humor."
"We are all mourning his passing -- his family, his friends and colleagues are in our thoughts," he said.