NEW YORK (BLOOMBERG) - An error at Nasdaq's computer systems caused confusion among traders on Monday (July 3), as Wall Street closed early for the July 4 holiday.

The exchange operator was conducting a test of its pricing data feed that led to some third-party providers showing wild moves in shares including Google and Microsoft that never occurred, according to spokesman Joe Christinat. Nasdaq is working with the providers to resolve the issue, he said.

The apparent swings came on a day that the US stock market closed three hours earlier than usual at 1pm. While Nasdaq's website said its systems were operating normally, trading screens around the world showed the likes of Amazon.com and Microsoft's shares appearing to fall by more than 50 per cent, while Apple's stock was at one stage looking as if it had risen 348 per cent. The data showed more than a dozen securities, including Nasdaq's own company stock, at the same price, US$123.47.

Nasdaq has had previous issues with its pricing data feed. In 2013, the exchange halted all trading in its listed stocks for about three hours because of a fault with the feed.

Bloomberg, the parent of this news organisation, distributes Nasdaq data and was among those affected.