Elon Musk says Tesla will double its Full Self-Driving software's beta program. It comes amid news that Ford's Mustang Mach-E is eating into Tesla's US sales.

• CEO Elon Musk said Tesla would double a beta testing program for its Full Self-Driving software.
• "Still be careful, but it's getting mature," Musk said.
• The news comes amid reports that a Ford rival is eating into Tesla's lead in the EV market.

Tesla CEO Elon Musk on Friday said the carmaker would double a beta testing program for its self-driving software. The news comes amid reports that Ford's electric Mustang Mach-E seems to be eating into Tesla's lead in the electric vehicle market.

On Twitter, Musk said:"If you want the Tesla Full Self-Driving Beta downloaded to your car, let us know."

The beta drivers will be testing version 8.2 of the company's Full Self-Driving software, said Musk. Last week, the CEO said version 8.1 "normally drives me around with no interventions." The next version will be "a big step change beyond that."

"Still be careful, but it's getting mature," he added on Friday.

Musk also said he expected the beta program to be "probably" 10 times larger by the time the company tests its version 8.3 software. Version 8.3 has "literally ~1000 improvements" from the previous version, he tweeted, adding it "will take time to QA internally before release probably in two or three weeks."

Tesla has an ever-growing number of electric vehicle rivals, and while Ford sold only 3,739 of the new SUVs in February, Tesla's share of the US electric-car market fell to 69% in the same month. This was down from 81% in the prior year, a Morgan Stanley report found. What's more, the Mustang accounted for nearly all of Tesla's market-share losses, the bank said.

Tesla's beta testers will be trying out the company's Full Self-Driving software. One beta user posted a video of his Tesla driving 358 miles, from Los Angeles to Silicon Valley, without the driver intervening.

The company had plans to launch the autopilot software as a subscription service this year. Musk said this month that it would "for sure" launch before July.

Waymo CEO, John Krafcik, in January said Tesla's software can't compete with Waymo's autonomous software. Tesla's building cars with assisted driving, while Waymo's building cars that don't need drivers at all, he said.

"So no Tesla is not a competitor at all. They're a car company making a driver assist system. We're a company making a fully autonomous driver," Krafcik said.

Musk shot back on Twitter, saying Tesla had "better AI hardware and software than Waymo."