Ever since last Thursday, when the US stock market nose-dived 5 per cent in as many minutes and then rebounded with equal rapidity (see the first chart), investors have been asking whether such a freak 'flash crash' could hit the Hong Kong market.
Happily, the answer is no - or rather that should be no, not yet.
Most early reports blamed last week's sudden sell-off in US stocks on human error, a so-called 'fat finger' trade in which a trader accidently keyed in an order to sell billions instead of millions of shares. Some commentators suspected deliberate manipulation, and a few even suspected a terrorist attack on the US market.
But as the US regulators have sifted through the 17 million trades struck between 2pm and 3pm last Thursday in an attempt to work out exactly what happened and why, it has become apparent that the likely causes of the slump were more complex - and in many ways even more unsettling.
Clearly a major contributory factor in the sell-off was the enormous changes that have taken place in the US market over recent years. As new technologies have developed, a whole suite of alternative trading mechanisms have emerged to challenge the dominance of the established stock exchanges. Today dozens of electronic platforms offer investors and dealers the chance to trade huge blocks of shares in a matter of milliseconds.
Among the results has been an explosion in volumes - over 10 billion shares in NYSE-listed companies were traded last Thursday, compared with just 600 million during the 1987 market crash.
But recent changes have also led to a fragmentation of the market. Five years ago, the NYSE captured 79 per cent of trades in its own listed stocks. Last year it got 25 per cent. Today its overall market share is estimated at just 15 per cent (see the second chart).