"The first tunnel is almost done," Musk tweeted to his 23.1 million followers shortly after 5 p.m.
Musk's Boring Co. is building the tunnel beneath the city of Hawthorne, part of his grand vision for a transportation network that whisks commuters across the county. Last year, Hawthorne officials approved the Boring Co.'s request to tunnel west from Space X headquarters. At the time, they said the tunnel had extended 500 feet.
The company has said its technology could move vehicles, as well as pods carrying passengers and bicyclists, through tunnels at speeds of up to 130 mph.
A video simulation released by the company last year shows a driver steering a vehicle onto a car-sized platform on the street, parallel to the curb. The platform, called a skate, sinks like an elevator, then carries the car through the tunnel.
In subsequent tweets Musk said there would be an opening event on the night of Dec. 10 and free rides for the public the next day.
When asked if the date represented real time or "Elon time," the entrepreneur wrote, "I think real."