The hospital treating ailing Chinese dissident Liu Xiaobo has said his condition is now critical and doctors are in "active rescue".

Shenyang's First Hospital of China Medical University said on Monday that Liu, who has late-stage liver cancer, is suffering from a severely swollen stomach, low blood pressure and poor kidney function.

Doctors also said Liu's tumour has grown and his liver is bleeding.

China has come under international pressure to let its most prominent dissident leave the country for treatment, but Chinese doctors said over the weekend that Liu was too sick to travel.

German and US doctors who visited Liu, however, said on Sunday that they deemed him strong enough to be evacuated. The doctors said any evacuation would have to take place "as quickly as possible" before Liu's condition deteriorates further.

READ MORE: Liu Xiaobo can be taken overseas, foreign medics say

Liu, 61, was diagnosed with liver cancer in May while serving an 11-year sentence for inciting subversion after he helped to write a petition known as "Charter 08" calling for basic human rights and sweeping political reforms.

The Nobel Peace Prize laureate was recently moved from jail to a hospital in Shenyang to be treated.

Beijing has come under fire from rights groups over its treatment of Liu and for waiting until he became terminally ill to release him from prison.