NEW YORK, Oct 21 (Reuters) - A company owned by Elon Musk that is trying to lower the cost of building high-speed transit tunnels is nearing completion on the first tunnel, Musk said on Twitter on Sunday.

The first tunnel, under Hawthorne in the Los Angeles area, is almost done and will open on Dec. 10, Musk said. Privately held Boring Co has been promoting its plans for tunnels that would allow high-speed travel between cities. (Reporting by Jessica Resnick-Ault; Editing by Sandra Maler)