"California pulling back its reopening plans and US tensions with China are causing some profit-taking in the more volatile stocks locally," he said.
Vista Group International has been among those whipped around by global fears over Covid. It fell 6.3 per cent to $1.20. Tourism Holdings declined 2.8 per cent to $1.77.
Fishing company Sanford led the market higher, rising 4.4 per cent to $6.60 on a typically light volume of 31,000 shares.
Chorus increased 3.9 per cent to $7.55, extending its recovery from a pull back on Friday when the Commerce Commission suggested it would change the way the internet infrastructure firm can recognise losses.
Trethewey said investors were getting more comfortable with the commission's announcement, and the stock has recovered 6.8 per cent this week after it dropped 8 per cent on Friday. Spark New Zealand, the network operator's biggest customer, rose 2.2 per cent to $4.805.
SkyCity Entertainment Group rose 3.4 per cent to $2.47 and Synlait Milk advanced 3 per cent to $7.26.
The property sector saw strong gains with local tenants better able to make rents and property prices holding steady for now.
Goodman Property Trust climbed 2.8 per cent to $2.22, Investore Property advanced 2.7 per cent to $1.91, Precinct Properties New Zealand rose 1.8 per cent to $1.68 and Kiwi Property Group was up 1 per cent at $1.035.
F&P Healthcare increased 1.7 per cent at $36.20 and A2 Milk rose 1.1 per cent $20.93 - both stocks have benefitted through the lockdowns and may continue to do so.
Pushpay Holdings posted the day's biggest decline, falling 8.4 per cent to $8.46 after cornerstone shareholders, the Huljich family, sold a quarter of their stake, or 14.4 million shares, in an overnight block trade at $8.60 apiece for $123.8m in total.
"The stock has been a beneficiary of Covid and has run very hot over the last couple of months, so it is not surprising to see some of the large holders take some money off the table," Trethewey said.
"They have been large holders for a long time and have retained 75 per cent of their stake."
Metlifecare rose 0.2 per cent to $5.89. The company is under a takeover offer by EQT Group, which had tried to walk away from an earlier deal at $7 per share, only to be threatened with litigation.
"It is trading at a very tight premium to the $6 price which reflects a reasonable level of expectation that the deal will be done," Trethewey said.