Large numbers of Google's Gmail web addresses were reportedly blocked in China over the weekend.
The disruption occurred on Friday, according to GreatFire.org, a China-based freedom of speech group.
One Gmail user complained on Twitter yesterday that domestic suppliers could not send emails to Gmail accounts and described the block as "way too harsh," according to Google Translate.
"I think the government is just trying to further eliminate Google's presence in China and even weaken its market overseas," a member of GreatFire.org told Reuters news service.
"Imagine if Gmail users might not get through to Chinese clients. Many people outside China might be forced to switch away from Gmail."
According to Google's Transparency Report, traffic nose-dived on Thursday.
Chinese Foreign Ministry spokeswoman Hua Chunying told Reuters she was not aware Gmail had been blocked.
"China has consistently had a welcoming and supportive attitude towards foreign investors doing legitimate business here," she said. "We will, as always, provide an open, transparent and good environment for foreign companies in China."
But the majority of Google's services have been disrupted in China since June this year, the month marking the 25th anniversary of the Tiananmen Square uprising.
China is one of five regions reported to have recent or ongoing disruptions to Google services. The others are Iran, Iraq, Pakistan and Turkey. ®