Gmail has been entirely blocked in China, with the country’s firewall being blamed after months of disruptions to the world’s biggest email service which is run by Google.

The country has been disrupting Google services since the summer, in the run-up to the 25th anniversary of the government’s crackdown on demonstrations in Tiananmen Square.

The takedown could cause huge problems for China’s companies, many of which run their corporate email accounts through Gmail.

Large numbers of Gmail web addresses were cut off in China on Friday, said GreatFire.org, a China-based freedom of speech advocacy group. Users said the service was still down on Monday.

"I think the government is just trying to further eliminate Google's presence in China and even weaken its market overseas," said a member of GreatFire.org, who uses a pseudonym.

Google's own Transparency Report, which shows real-time traffic to Google services, displayed a sharp drop-off in traffic to Gmail from China on Friday.

"We've checked and there's nothing wrong on our end," a Singapore-based spokesman for Google said in an email.

China maintains tight control over the internet, nipping in the bud any signs of dissent or challenges to the ruling Communist Party's leadership.

The country is host to the world's most sophisticated internet censorship mechanism, known as the Great Firewall of China. Critics say China has stepped up its disruption of foreign online services like Google over the past year to create an internet cut off from the rest of the world.

Chinese Foreign Ministry spokeswoman Hua Chunying said she did not know anything about Gmail being blocked, adding that the government was committed to providing a good business environment for foreign investors.

"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."

One popular way for companies and people to get around China's internet censorship is to use a Virtual Private Network (VPN) which allows unhindered access to blocked sites and services.

"It's becoming harder and harder to connect and do work in China when services like Gmail are being blocked," said Zach Smith, a Beijing-based digital products manager at City Weekend magazine. "Using a VPN seems to be the only answer to doing anything these days online in China."