Access to cyberspace was hindered for more than two hours on the mainland yesterday, as virtually all foreign websites were inaccessible - with no official explanation.
At the same time, internet users outside the mainland, including in Hong Kong, reported they couldn't access mainland-based websites.
Some mainland internet analysts speculated the problem was probably due to a serious hardware malfunction afflicting major internet service providers.
Connections to websites in overseas regions or countries, including Hong Kong, Japan, South Korea, the United States, the Netherlands, Singapore and Australia were cut off at around 10.40am, according to a report on Ccidnet.com, a mainland-based IT industry portal.
Most mainland internet users were relieved as web access was gradually restored to normal after about 1pm, but some remained sceptical of the cause, as neither service providers nor the government offered an explanation.
In an attempt to determine the source of the problem, network engineers for Ccidnet.com tried to connect to a server in the US using a China Telecom server in Xuzhou, Jiangsu, the site's report said. But despite repeated attempts, not a single packet of data could be sent or received.
Using specialised software, the engineers traced the problem to a bottleneck involving two routers in Shanghai, a major hub that connects mainland and overseas cables. Data traffic at the juncture was found to have become suddenly congested.