"There's big money out there running the numbers on this and the reaction is pretty fierce," said Grant Davies, an investment advisor at Hamilton Hindin Greene.
"The share prices have been such that there's something to give back and they're only going back to where they were at the end of August."
Those power companies are all among the country's top 20 stocks and weighed on the broader index, which was the worst performer across Asia. South Port New Zealand, which counts the smelter as its biggest freight customer, slipped 0.6 per cent to $7.85.
SkyCity Entertainment Group was down 0.5 per cent at $3.85 as the fire at the international convention centre building site raged on for a second day. Lead contractor Fletcher Building rose 1.3 per cent to $4.71, with 2.3 million shares changing hands. The chief executives of both companies fronted a briefing today, saying it was too early to make any judgements on the extent of the damage and that they were both covered by insurance.
Davies said the companies unexpectedly outperformed the broader index today, but that there were still many unknowns.
"We still don't know what the damage is, but it looks pretty extensive," he said.
Tourism Holdings declined 1.9 per cent to $3.58 after it postponed its annual meeting in downtown Auckland because of the fire.
Synlait Milk posted the day's biggest gain, up 3 per cent at $9.78 on a volume of 59,000 shares, less than its 78,000 average. Ebos Group rose 1.6 per cent to $25 and Pushpay Holdings increased 1.3 per cent to $3.24.
Of other stocks trading on volumes of more than a million shares, Spark New Zealand fell 3.2 per cent to $4.415, Freightways declined 1 per cent to $7.90, Precinct Properties New Zealand was unchanged at $1.88 and Kiwi Property Group was unchanged at $1.67.
Auckland International Airport fell 1.8 per cent to $9 after affirming earnings and capital spending guidance at today's annual meeting.
Air New Zealand decreased 0.7 per cent to $2.805 after saying it would drop its Los Angeles-London route in October next year, and at the same time introduce an Auckland-New York route.
Property For Industry fell 1 per cent to $2.425 after it said it sold an Albany property for $33m as part of a planned sale programme of non-industrial properties.
NZX slipped 0.8 per cent to $1.27 after it reported a 13 per cent increase in third-quarter revenue from continuing operations. Year-to-date revenue was down 1.5 per cent at $51.2m due to the year-earlier period including revenue from the now-sold, AgriHQ, Farmers Weekly and Australian Grain Information Unit businesses.
Outside the benchmark index, Serko dropped 11 per cent to $3.42 before trading was halted. The dual-listed travel booking software developer told the ASX that it was at an advanced stage of finalising a material transaction that included a proposed capital raising.
Augusta Capital fell 1.9 per cent to $1.57 after it said it expected first-half earnings to be materially lower than the prior year due to a lack of capital raisings, and two developments that needed investment.
Vital, formerly TeamTalk, declined 2.2 per cent to 88 cents after it said earnings before interest, tax, depreciation and amortisation would be $8.7-11m in the year ending June 30, 2020, down from the $11.1m reported in 2019. The downgrade reflected the extra cost of transforming the business and switching customers to new networks.
TIL Logistics was unchanged at $1.19 after it told shareholders it expected a better performance in the 2020 financial year on organic growth, new customers, and extra warehousing capacity, despite a softer business environment.
