Corrupt data that accidentally flowed out of a NASDAQ systems test caused the share prices of some of the world's largest companies swing as much as 80 per cent in either direction in after hours trading on Monday.

Traders were left gawping at their Bloomberg and Reuters terminals, which showed the likes of Amazon and Microsoft plummet more than 50 per cent and Apple rocket as much as 348 per cent higher, before the trio settled on a price of $US123.47. 

The error gave Apple a theoretical market capitalisation of $US3.4 trillion ($4.44 trillion), compared to the $US751 billion at which it was valued when trading closed on Friday.

Shares in Microsoft appeared to soar 79.1 per cent higher, while eBay had rocketed 253.5 per cent. Zynga, a mobile and social game maker, experienced a staggering 3,292 per cent leap. 

According to third data provider, Bloomberg, Nasdaq developers were testing the system on the eve of the US Independence Day holiday and accidentally sent "bad data" to the financial data providers.

"It's an exchange-side issue, where the Nasdaq disseminated bad data and traded corrupt messages to us during an exchange-side test of their systems," a Bloomberg spokeswoman told AFR, over the phone. 

"We were not notified of the test. But, we are no longer receiving these trade corrupt messages.

"We are now just working to correct the bad data."

The spokesperson was unable to confirm why the likes of Apple, Alphabet and Amazon were altered, whereas Facebook and some other listed stocks were unchanged.

The prices on Nasdaq's official website remained unaltered, however the pricings on Bloomberg, Thomson Reuters and Google Finance showed a raft of price changes to $US123.47.

In a statement, Nasdaq has said the glitch was related to "the improper use of test data" sent out to third party data providers and that it was working to resolve the matter. 

Any trades made with respect the clearly inaccurate pricing have been cancelled. 

According to the Financial Times, the exchange's full statement said: "Nasdaq is investigating the improper use of test data distributed by the UTP [Unlisted trading privileges] and consumed by third parties. As part of its normal process, the UTP distributed test data and certain third parties improperly propagated the data. Nasdaq is working with third party vendors to resolve the matter."

The sharp price movements dramatically repriced the likes of some companies in either direction. At one point Apple had a theoretical market capitalisation of $US3.4 trillion, as opposed to the $US751 billion valuation at Friday's close, and Bed Bath & Beyond was indicating a $US17.9 billion market valuation instead of $US4.4 billion.

Fairfax Media with wires