Apple staff and customers, wearing facemasks to protect against the COVID-19 coronavirus, are seen on the shop premises in Beijing on February 22, 2020.

All of Apple's retail stores in mainland China apart from four are now open after the coronavirus outbreak forced the iPhone maker to close its shops for an extended period of time.

The U.S. technology giant has 42 stores in China and 38 of those are open again. Several of those however are still running limited operating hours.

Three stores in Tianjin, a major city in northwest China, and a retail location in Suzhou, a city west of Shanghai, remain closed. An Apple spokesperson declined to comment on the reason for keeping those stores shut when contacted by CNBC.

China is a critical market for Apple. The iPhone-maker warned that it would not meet the already wider-than-usual revenue guidance it gave for the March quarter of $63 billion to $67 billion.