Friends of Nobel Peace Prize winner Liu Xiaobo, who died of liver cancer in custody, said that freedom of his widow, Liu Xia, is now a priority. Picture: AP Video via AP

Beijing - Friends of China's Nobel Peace Prize-winning dissident Liu Xiaobo, who died of liver cancer in custody, said on Friday they are still unable to contact his widow, Liu Xia, and that ensuring her freedom is now a top priority.

Liu Xiaobo, 61, was jailed for 11 years in 2009 for "inciting subversion of state power" after he helped write a petition known as "Charter 08" calling for sweeping political reforms.

Liu Xia has been under effective house arrest since her husband won the Nobel Peace Prize in 2010 and was allowed to visit him in prison about once a month. She suffers from depression.

Liu Xiaobo died on Thursday after suffering multiple organ failure. He was recently moved from jail to a hospital in the northeastern city of Shenyang to be treated for late-stage liver cancer.

Rights groups and Western governments have mourned Liu Xiaobo's death and also called for Chinese authorities to allow his wife and the rest of his family to move around freely.

United Nations High Commissioner for Human Rights Zeid Ra'ad Al Hussein also urged China to guarantee Liu Xia freedom of movement, and allow her to travel abroad should she want to.

China, however, said the case remained an internal matter.

"The handling of Liu Xiaobo's case belongs to China's domestic affairs, and foreign countries are in no position to make improper remarks," China's foreign ministry spokesperson Geng Shuang said in a statement sent to Reuters on Friday.

"We call on relevant countries to respect China's judicial sovereignty and not to meddle in China's domestic affairs with this individual case," he said.

Hu Jia, a fellow dissident and family friend, said Liu Xia's freedom was now a top priority for Liu Xiaobo's supporters.

"Now, we are most concerned about Liu Xia, but there has been no information about her. She is at this moment the person who is suffering most," Hu said.

"All the willpower and force we put behind freeing Liu Xiaobo, we have turned to Liu Xia," he said, calling on the United States and Germany to continue pressuring China to free Liu Xia.

Efforts should also focus on Liu Hui, the younger brother of Liu Xia, who was sentenced to 11 years in prison in 2013 for fraud and to whom Liu Xia is very close, Hu said.

Several other family friends also confirmed that they were still unable to contact Liu Xia or other members of Liu's family to confirm her whereabouts.

Shanghai-based writer Wen Kejian, another friend of the Liu family, said his supporters would "pay very close attention to Liu Xia's freedom".

"I think, no matter what, she should be granted complete and unconditional freedom," Wen said.

Friends have also begun calling to be allowed to participate in Liu Xiaobo's funeral arrangements and support his wife and family.

More than 150 friends and supporters, including some of China's most prominent dissidents, rights lawyers and intellectuals, have also signed an open letter announcing plans for an "online memorial" to Liu.

Signatories have urged authorities to release Liu's body and allow an open funeral by his family and friends.

"We will pay close attention to how Liu Xiaobo's funeral will be arranged," said writer Wen Kejian. "We, at the very least, hope to have the opportunity to go to Shenyang or Beijing to send him off."

Rights lawyer Chen Jinxue added, "Normally if someone has passed, the right to deal with the body lies with the family."

An outpouring of grief met the news of Liu's death, with many liberals, lawyers, dissidents and journalists sharing articles and posting on popular instant messaging app WeChat.

But censors were swift to act. Even an article titled, "Speaking of heroes, who is a hero?" from respected business publication Caixin was taken down after being shared by many of Liu Xiaobo's supporters, despite making no mention of him.

Ye Du, a writer and friend of Liu's, said he hoped people would be able to commemorate Liu Xiaobo, despite harsh government restrictions.

"Liu Xia will surely be monitored and controlled," he added. "Grieving in reality will certainly also be strictly controlled, but there will definitely be lots of people who will use all sorts of ways to mourn."