Every day Li Wenzu's son asks her why his daddy has not come home, she says. Her husband went missing six months ago in a sweeping crackdown on Chinese human rights lawyers, but she tells the three-year-old he is on a "business trip".

Her husband Wang Quanzhang was among more than 130 legal staff -- along with around 70 activists -- taken away by police in a July sweep aimed at courtroom critics of Communist authorities.

She only learned that he had been detained from a television broadcast labelling his law firm as rabble-rousing criminals.

Now she is on a desperate and fruitless search for answers from officials.

Wearing black, she wiped a stream of tears from her cheeks with a napkin, as their child toyed with a mobile phone.

"I cry every day," she said. "Our lives have been turned upside down."

At least 16 lawyers and their colleagues remain detained, most under a form of detention that allows them to be held at locations outside official facilities for six months -- so it should technically expire this weekend.

Chinese law also authorises those suspected of state security offences to be held in isolation from the outside world, effectively enabling authorities to legally make people disappear.

- 'All darkness' -

Two defence lawyers Li appointed told her they were forced to withdraw their services after government intimidation.

Eventually attorneys received a notice indicating he was held in the northern city of Tianjin, but could not be visited on "state security" grounds.

A string of visits to the city by his lawyers and relatives have proved fruitless.

"For these months, we have always been trying to use legal means, but to no avail," she said. "The current legal environment is like Beijing's pollution, all darkness with no sunlight.

"We are under a lot of economic pressure, which is painful. But the main thing is we are terrified for his personal safety," Li added.

On Thursday about a dozen relatives and their lawyers gathered in blistering cold outside the Hexi District Detention Centre in Tianjin, in yet another attempt to seek answers -- but were met with a wall of silence.

"If they are not released we will fight on," Li declared. "Yesterday when I left home I was followed, there is nothing I could do but leave my child at home," she added.

The three-year-old is not the only child to suffer in the crackdown -- Bao Zhuoxuan, 16, whose mother Wang Yu is among the detained lawyers, is also being held under a form of house arrest, friends say.

The teenager was seized in October after trying to escape China overland to neighbouring Myanmar, state-run media said.

State television showed Wang and her husband -- also a detained lawyer -- breaking down in tears on hearing the news of their son's capture.

- 'Worries, disappointment, pain' -

Among the missing are two legal assistants in their twenties.

Working to defend some of China's most vulnerable people seemed natural for one of them -- 24-year-old Zhao Wei, who cooked meals for HIV/Aids patients at university, and had taken part in feminist protests for more women's toilets, her husband You Minglei told AFP.

A state security agent travelled some 1,400 kilometres (900 miles) with him from his hometown to Tianjin as he tried to seek answers, and insisted on sleeping in the same hotel room.

"It was one room, two beds," he said.

In an account posted on the Internet which she confirmed to AFP, Zhao's mother described travelling to Tianjin for her daughter's 24th birthday, some 100 days after she went missing.

"I had massive worries, disappointment and pain, there was no way to express my feelings in words," she said.

"I said it's my daughter's birthday, I want to give her a cake and some clothes. Policeman Zhao said: that's not permitted," she added, referring to the policeman she met at the scene.

"I told policeman Zhao I was looking for my daughter. I asked: 'What crime has she committed?' He answered: 'Don't you watch television?'"