Staff at the Beijing bureau said they had not been affected because the office had access to an overseas server.

But across the mainland, access was sporadic. It was unavailable in Beijing's business district all day, but the site was accessible just a few miles away.

'It's fine here. I can navigate the whole site,' said David Hodges, an expatriate freelance writer.

The interference began after the Foreign Ministry on Wednesday summoned CNN's Beijing bureau chief for a dressing down. The ministry rejected an apology over earlier remarks by one of its US-based commentators, Jack Cafferty.

During an edition of The Situation Room on April 9, Cafferty called China's leaders 'goons' and the country's exports 'junk'.

Foreign Ministry spokeswoman Jiang Yu rejected the apology as 'insincere'.

Many mainlanders have participated in an anti-CNN campaign, which began following its coverage of the Tibetan riots last month.

And they also appeared to have sparked activity by sympathetic hackers and scathing blogs.

Online rumours spread yesterday that CNN.com had either been hacked or blocked by mainland censors.

An Australia-based IT news site, computerworld.com.au reported that Chinese hackers known as the Red Hacker Alliance were plotting an attack on CNN.com today.

But the trouble accessing the website yesterday suggested the assault had begun ahead of schedule.

'This is not an apology. They think we Chinese are idiots? They have just insulted us further. Not acceptable at all,' one commenter, 'Lizchn', said in a thread entitled 'CNN's weak apology on the Cafferty matter'.

Additional reporting by Charlie Gidney in Hong Kong