The SpaceX founder made his warning on the Sway podcast, where he reiterated his fears the Sun will engulf the Earth one day. Mr Musk has touted his company as making getting humans to Mars its top priority. He previously claimed SpaceX flights to the planet would be possible “in our lifetimes”.
During the interview, Mr Musk said a solar disaster will destroy the Earth in the future, and pushed for humanity to become an “interplanetary species”.
He said: “Eventually the sun is going to expand and engulf Earth.”
While he claimed the Earth’s destruction “is for sure going to happen”, he reassured the hosts it won’t be “anytime soon”.
Mr Musk’s statements echo scientists who believe the Sun will expand and swallow the Solar System in the next six billion years, destroying the Earth.
After the grim warning, Mr Musk promoted SpaceX spacecraft, and said the fleet could help humanity move to Mars.
SpaceX’s Starship is designed for deep space travel, and is being developed at a Texas facility.
He told Sway the key step for travel to Mars is “a fully and rapidly reusable rocket”.
He added human flights on Starship could launch within two years, and said: “I think we will launch Starship sometime next year, close to August. We will run it in automatic mode, without people.
“I think it will be safe for people in two years, but definitely three years.”
But Mr Musk also warned a city on Mars could be deadly if it doesn’t work properly.
He said: “I want to emphasise that this is a very hard and dangerous, difficult thing, not for the faint of heart.
“Good chance you’ll die, it’s going to be tough going, but it will be pretty glorious if it works out.”
He also touted “progress” with the Starship rocket, and added: “We’re rapidly making more and more ships and we will be starting on the booster soon.
“It’s scaling up the production system which is the hard part, and we are making progress on that.”
The Starship prototype was unveiled in September last year, with Mr Musk tempering expectations of a fast turnaround on pace travel.
He said at the announcement: “Nobody has ever made a fully reusable, orbital rocket.”
SpaceX also successfully completed its second “hop” test of a Starship rocket tank prototype earlier this month.
The rocket used a prototype Raptor engine developed by the company, and launched 500 feet into the air.