Four of the five Hong Kong booksellers who went missing in October appeared on Chinese television confirming for the first time they'd been detained for "illegal book trading" in mainland China.

The five booksellers — including a British and Swedish national — had been linked to the same Hong Kong publisher and bookstore that specialised in gossipy books on the private lives and power struggles of China's Communist Party leaders.

The disappearances have prompted fears that mainland Chinese authorities may be using shadowy tactics that erode the "one country, two systems" formula under which Hong Kong has been governed since its return to China from British rule in 1997.

Four of the men, Gui Minhai, Lui Por, Cheung Chi-ping and Lam Wing-kee, gave details of their alleged offences to Phoenix Television on Sunday night.

"I have deeply reflected on what I have done and very much regret the illegal book trading I have carried out with Gui Minhai," said Lui Por in the Phoenix TV report.

In a four-minute report that involved exclusive interviews with the four, they confessed to selling "unauthorized" books in China via an online platform and evading customs inspections to deliver some 4000 books to 380 customers since October 2014.

Gui said he'd altered and obscured the covers of the Hong Kong-printed books with nylon bags to "evade" customs security checks and was singled out by the others as the mastermind. The group had also opened a bank account in China to make payments.

Gui had previously confessed on Chinese state television to a fatal drink-driving incident over a decade ago, after going missing in Thailand late last year.

International outcry

The TV report also detailed how Lui, Cheung and Lee had been arrested by Chinese authorities in Shenzhen and Dongguan, two cities in southern China close to Hong Kong, in October and then called upon to testify in the case.

"I know that Gui Minhai's books are fabricated. They were downloaded from the Internet, and were pieced together from magazines," said Lam. "They have generated lots of rumours in society and brought a bad influence ... I deeply acknowledge my mistakes and am willing to be penalized," Lam added.

The only bookseller not to appear in the report was Lee Bo, a British passport holder, who Britain said had been "involuntarily removed" to China from Hong Kong in late December, constituting a "serious breach" of the one country, two systems formula.

A number of governments have expressed concern regarding the disappearances, which some diplomats fear were abductions by Chinese agents in Hong Kong and Thailand.

China's Foreign Ministry, however, has said its law enforcement officials would never do anything illegal, especially not overseas, and called on foreign governments not to interfere in Hong Kong affairs.

Foreign Ministry spokesman Hong Lei acknowledged the television report in a daily briefing, saying the men had "already admitted to their actions", without elaborating. The Phoenix television report said Lam, Lui and Cheung might be allowed to return to Hong Kong this week, citing unspecified sources. Gui, however, was expected to remain in detention.

A Swedish Foreign Ministry spokeswoman told Reuters by telephone that an envoy had visited Gui on Wednesday and that his condition is "very good," but gave no further details. Britain has not yet been granted consular access to Lee despite formal requests to China, a spokesperson for the British consulate in Hong Kong told Reuters.

A Phoenix Television spokeswoman said it was granted access to the men after making "numerous requests to the relevant authorities" but declined to give further details on where, when or under what conditions the interviews were conducted.