SpaceX shares jumped in their second day of trading, adding to gains following a blockbuster debut that instantly vaulted it into the ranks of the world's most valuable public companies. The stock climbed as much as 11%, extending Friday's 19% rally. The move boosts the company's market value to more than $2.3 trillion, putting it among the top six largest companies in the world. At its current market capitalisation, it's less than $400 billion away from overtaking Amazon.com, which boasts a $2.7 trillion value.SpaceX has exercised the IPO's over-allotment option, which lets underwriters sell an additional 83.3 million shares, according to a statement Monday. The so-called greenshoe increases the amount raised to $86.2 billion, or $85.7 billion after subtracting the $500 million of underwriting expenses listed in the prospectus.On Monday, the Dow Jones Industrial Average hit a record high, rising 638.83 points, or 1.24%, to 51,839.01. The S&P 500 was up 128.52 points, or 1.73%, at 7,559.98 and the Nasdaq was up 692.81 points, or 2.68%, at 26,581.72, at the time of going to press.