"The facility is currently operating at significantly reduced capacity," Apple said in a statement without elaborating how much production has been impacted.
"We continue to see strong demand for iPhone 14 Pro and iPhone 14 Pro Max models. However, we now expect lower iPhone 14 Pro and iPhone 14 Pro Max shipments than we previously anticipated," it said.
Reuters last month reported that production of Apple's iPhones could slump by as much as 30% at one of the world's biggest factories in November due to tightening Covid-19 curbs in China.
Its main Zhengzhou plant in central China, which employs about 200,000 people, has been rocked by discontent over stringent measures to curb the spread of Covid-19, with many workers fleeing the site.
Market research firm TrendForce said last week it has cut its iPhone shipments forecast for the December quarter by 2-3 million units, from 80 million previously, due to the troubles at the Zhengzhou plant, adding that its investigation of the situation found that the factory's capacity utilisation rates were now around 70%.
Apple, which launched sales of the new iPhones in September, said customers will experience longer wait times to receive their new products.
"Anything that affects Apple's production obviously affects their share price," said Quincy Krosby, chief global strategist at LPL Financial in Charlotte, North Carolina.
"But this is part of a much deeper story - the uncertainty surrounding the future of the Chinese economy... These headlines are part of the ongoing saga as to whether there is any truth to the consistent rumours that authorities are discussing whether some of the measures will be lifted in the first quarter."
China on Sunday reported its highest number of new Covid-19 infections in six months, a day after health officials said they were sticking with strict coronavirus curbs, likely disappointing recent investor hopes for an easing.
Foxconn cuts outlook
Taiwan's Foxconn, the operator of the Zhengzhou factory, said on Monday it was working to resume full production at the plant as soon as possible, and revised down its fourth quarter outlook.
It said it would implement new measures at the plant to curb the spread of Covid-19, which include a system that restricts factory workers' movement.
China ordered an industrial park that houses the iPhone factory to enter a seven-day lockdown on Wednesday, in a move set to intensify pressure on the Apple supplier as it scrambles to quell worker discontent at the base.
The Zhengzhou Airport Economy Zone in central China said it would impose "silent management" measures with immediate effect, including barring all residents from going out and only allowing approved vehicles on roads within that area.
Foxconn, the world's largest contract electronics maker, said in a statement that the provincial government in Henan, where Zhengzhou is located, "has made it clear that it will, as always, fully support Foxconn in Henan".
"Foxconn is now working with the government in concerted effort to stamp out the pandemic and resume production to its full capacity as quickly as possible."
Foxconn, formally Hon Hai Precision Industry Co Ltd, is Apple's biggest iPhone maker, accounting for 70% of iPhone shipments globally. It has other smaller production sites in India and southern China.
Having previously guided for "cautious optimism" in the fourth quarter, Foxconn said it will "revise down" its outlook given events in Zhengzhou.
The fourth quarter is traditionally the hot season for Taiwan's tech companies as they race to supply cellphones, tablets and other electronics for the year-end holiday period in Western markets.
Foxconn releases third-quarter earnings on Nov. 10.