"Clearly at the last auction the market was struggling to digest that [volume] and I don't think the price action is going to be favourable."
New Zealand's wholemilk powder and milkfat products looked to be below the cost of production for all major producers and in the "affordable zone" for price-sensitive low-income countries, Williams said.
"This doesn't seem to mean too much at present with the market struggling to digest higher seasonal volumes from New Zealand."
China remained largely absent and many other markets in Africa, the Middle East and Asia seemed to have covered immediate requirements through increased imports.
Auction volumes are broadly unchanged for this week's event.
However, August offered volumes nearly double and stay at [those] high levels for the next seven or eight auctions.
NZX futures pricing for skim milk powder, anhydrous milkfat and butter are pointing to gains of 8-10 per cent which would imply little change to the GDT-Trade Weighted Index on Thursday.
ASB Bank rural economist Nathan Penny said Chinese stock market falls were weighing down commodity prices.
"In particular and most visibly, dairy prices are under pressure," Penny said.
The Chinese stock market concerns are likely to have contributed to the price weakness at the July 2 auction, when overall prices - measured by the GDT Index - fell by 5.9 per cent and wholemilk powder prices dropped by 10.8 per cent.
"With the stockmarket concerns heightening since then, another fall is on the cards at the July 15 auction," Penny said.
"Current milk futures pricing suggests a fall of similar magnitude to the last auction."