Spark New Zealand was the best performer, up 1.2 per cent to $3.915, while Fletcher Building dropped 0.6 per cent to $7.92, after falling as low as $7.82 in the first hour.
The benchmark index has been hitting record highs recently, and is still up 13 per cent so far this year, and Williamson said today could just be some buyers taking profit ahead of the mid-year reporting season.
"If the market does have a correction on relatively light volume it shows there's not a lot of selling, just a case of buyers being patient and sitting back a bit," he said.
All three companies reporting on Monday joined in today's sell-off. Contact Energy fell 1.3 per cent to $5.38, Heartland Bank declined 1.1 per cent to $1.86 and Freightways was down 0.6 per cent to $8.10.
Outside the benchmark index, Hallenstein Glasson Holdings gained 3.1 per cent to $3.29. The clothing retailer posted a 7 per cent increase in annual sales and said profit was up about 25 per cent on the previous year.