Apple has cut the revenue forecast for its latest quarter, citing fewer iPhone upgrades and weak sales in China, and its shares tumbled in after-hours trade.

The company forecast $84 billion (USD) in revenue for its fiscal first quarter ended Dec. 29, which is below analysts' estimate of $91.5 billion, according to IBES data from Refinitiv. Apple originally forecast revenue of between $89 billion and $93 billion.

Wednesday was the first time that Apple issued a warning on its revenue guidance ahead of releasing quarterly results since the iPhone was launched in 2007.

Apple shares, which had been halted ahead of the announcement, skidded 7.7 percent in after-hours trade Wednesday, dragging the company's market value below $700 billion.

A slew of brokerages reduced their first-quarter production estimates for iPhones after several component makers in November forecast weaker-than-expected sales, leading some market watchers to call the peak for iPhones in several key markets.

On Apple's earnings call in November, Cook cited slowing growth in emerging markets such as Brazil, India and Russia for the lower-than-anticipated sales estimates for the company's fiscal first quarter. But Cook specifically said he "would not put China in that category" of countries with troubled growth.