Apple, Alphabet, Microsoft and Amazon share prices swing wildly as trading closes early

Shares in US tech giants have swung wildly in after-hours trading in what is likely to be an error from a third-party data provider.

Companies like Apple, Amazon, Microsoft and Google's parent company Alphabet were affected and at one point, all had their share prices changed to US$123.47, according to Bloomberg.

After-hours trading on the US stock market, NASDAQ, saw Apple's stock trading 348 percent higher than usual, giving it a theoretical market capitalisation of nearly US$3.4 trillion (A$4.5 trillion).

The wild swings caused some companies to enter into a trading halt. Bloomberg said it was unclear whether shares changed hands at these irregular prices.

The NASDAQ's own website did not display any irregularities, and a system status message showed that the system was operating normally. Third-party data providers such as Google Finance and Yahoo Finance displayed the altered information.

The NASDAQ closed early on Monday for the 4 July holiday in the US, a possible reason for the event. NASDAQ is yet to comment, according to Bloomberg.