Tesla shares sank in premarket trading Friday following the unveiling of its "Cybercab" autonomous taxi and a larger "Robovan" at the electric vehicle maker's "We, Robot" event.

Tesla Inc. unveiled its much-awaited robotaxi at an event in Southern California on Thursday night, showing a prototype of the Cybercab, an autonomous vehicle without steering wheels or pedals that Chief Executive Elon Musk said would cost less than $30,