Tesla Motors' plan to make 500,000 cars per year by 2018 — two years ahead of schedule — was too bold for some on Wall Street.

Many analysts expressed doubts that the company has the cash or the manufacturing expertise to pull it off. Tesla sold just 50,000 vehicles last year.

Tesla's shares dropped 5 percent to $212.53 Thursday.

Naysayers pointed to Tesla's significant issues with bringing vehicles to market. The Model X SUV, Tesla's latest vehicle, was delayed by more than 18 months.

CEO Elon Musk says Tesla needs to speed up production because of robust demand for the lower-cost Model 3, set to go on sale in late 2017. Musk says the Model 3 will be easier to build than the more complex Model X.