Leyla Guven, 55, launched a hunger strike on November 8 in protest at the prison conditions for Kurdish leader Abdullah Ocalan.

Ocalan is one of the founders of the outlawed Kurdistan Workers' Party (PKK) which has waged a bloody insurgency against the Turkish state since 1984, and which is blacklisted as a terror group by Ankara and its Western allies.

He has been serving a life sentence for treason in an island prison near Istanbul since his capture in 1999.

Guven launched her action to pressure the government into allowing lawyers and family members to visit Ocalan.

She was arrested in January 2018 for her criticism of Turkey's military operation against Kurdish militia forces in Syria and was jailed in the Kurdish majority city of Diyarbakir in southeastern Turkey pending trial.

The HDP remains under the scrutiny of Turkish authorities, which accuse the party of links to the PKK. Several of its MPs are behind bars, including former party leader Selahattin Demirtas.

Guven, whose hunger strike is supported by scores of detainees in prisons across Turkey, can no longer consume any liquids, including water, the party said in a statement.

Hunger strikers in Turkey usually take sugared or salted water and vitamins to prolong their fast.

The HDP said Guven was unable to meet with her lawyers because she could not walk to the visiting room.

"Guven, who has lost about 15 kilogrammes (33 pounds), cannot meet her needs or walk alone," it said, adding that she has started having problems such as aphasia, sensitivity to sound and light, and is often close to losing consciousness.

"Leyla Guven's situation has reached a critical stage that cannot be delayed, ignored or neglected for even an hour."

At least 171 prisoners are on hunger strike, according to the party, urging the international community to "urgently act and show their democratic reaction".

In 2012, hundreds of Kurdish prisoners ended a 68-day hunger strike after Ocalan urged them to do so.