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The authorities in Hong Kong have said they will not send a bookseller who was detained on the mainland back to China.

Hong Kong's security chief said there was no legal basis to transfer Lam Wing Kee, who worked for a publisher that sold books critical of China's leaders.

Chinese police say he is in breach of his bail terms and have threatened further action if he does not return.

Four other men who worked with Mr Lam were also held by China, prompting fears for freedom in Hong Kong.

Lam Wing Kee was seized in the Chinese city of Shenzhen last October.

He was allowed to return to Hong Kong in June. On his return he told a news conference that he had been kidnapped by an elite force in China, forced to confess and denied the right to see his family and a lawyer.

Media playback is unsupported on your device Media caption Lam Wing Kee was seized in the Chinese city of Shenzhen in October 2015

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On Tuesday the Ningbo public security bureau warned Mr Lam to return to the mainland "otherwise they will be forced to take other legal measures", state news agency Xinhua reported.

But Hong Kong's security chief Lai Tung-kwok insisted Mr Lam would not be sent back.

"There is no legal arrangement for the transfer of a person to the mainland authorities and the Hong Kong government will handle all cases in accordance with the law of Hong Kong," Mr Lai told reporters on Wednesday.

He made his comments a day after meeting Chinese officials in Beijing to discuss the case.

Under Hong Kong law, Chinese police do not have jurisdiction in Hong Kong, which is governed under the principle of "One Country, Two Systems".

But the case has sparked international concern that China could be attempting to rein in freedom of expression in Hong Kong.

Mighty Current publishing house disappearances

1. Lui Bo, general manager. Went missing: Shenzhen, 15 October 2015 Returned: March 2016

2. Cheung Jiping, business manager. Went missing: Dongguan, 15 October Returned: March 2016

3. Gui Minhai, co-owner. Went missing: Thailand, 17 October Still missing

4. Lam Wing Kee, manager. Went missing: Shenzhen, 23 October Returned: June 2016

5. Lee Bo, shareholder. Went missing: 30 December - he says from the mainland, Mr Lam says it was from Hong Kong Returned: March 2016