The freakish action bore hallmarks of past episodes in which computer malfunctions led to sudden price distortions. A US Securities and Exchange Commission spokesperson said the agency is looking into the matter.
On Tuesday, Walmart and McDonald’s were up and then down as much as 12 per cent before reverting to more normal trading ranges. By late in the session, the broad stock indexes were little changed.
Transactions occurred in NYSE-listed securities and took place on other platforms, including ones overseen by Nasdaq, CBOE Global Markets and private venues reporting to the Finra trade-reporting facility.
The start of trading in most American stocks involves a complicated but usually routine process called the opening auction, designed to limit volatility resulting from orders for shares that pile up before the start of the regular session. In it, a computer balances out supply and demand for a particular stock by establishing an opening price that can be viewed as the level that satisfies the largest possible number of traders.