Mr Liu died "peacefully" on Thursday afternoon, surrounded by his wife and other relatives, his main doctor Teng Yue'e said. His final words to Liu Xia were: "Live on well".
In a brief statement, officials said that Mr Liu had suffered multiple organ failure.
International powers press China
Calling the death "premature", the Nobel Committee said the Chinese refusal to allow him to travel was "deeply disturbing".
Germany, one of the countries considered as an option for Mr Liu, regretted that his transfer did not take place, Foreign Minister Sigmar Gabriel said.
"China now has the responsibility to quickly, transparently and plausibly answer the question of whether the cancer could not have been identified much earlier," he added in a statement.
British Foreign Secretary Boris Johnson also said it was "wrong" for China to have denied Liu Xiaobo permission to leave.
In the first official comment since his death, China's foreign ministry said: "The handling of Liu Xiaobo's case belongs to China's internal affairs, and foreign countries are in no position to make improper remarks," reported Xinhua state news agency on Friday.
Ministry spokesman Geng Shuang added that Chinese medical authorities had made all-out efforts to treat Mr Liu, Xinhua said.
The stern words are the latest development in the international controversy surrounding Mr Liu's case.
Chinese authorities announced last month that Mr Liu had liver cancer and moved him from prison to a hospital in the north-eastern city of Shenyang, where he was kept under heavy security.
In his final days, Western countries repeatedly urged China to give Mr Liu permission to seek palliative treatment elsewhere, which Beijing refused.
Chinese medical experts insisted he was too ill to travel, although Western doctors who examined him disagreed.
Image captionMr Liu's absence at the 2010 Nobel ceremony was marked by an empty chair
Germany, UK, France, and the United States are now calling on China to allow Liu Xia to travel and leave the country if she wished.
The call was endorsed by the UN High Commissioner for Human Rights, Zeid Ra'ad Al Hussein, who urged China to "guarantee Liu Xia's freedom of movement".
Mainland coverage muted
In mainland China, international reports on his death have been censored, and local media have carried virtually no reports apart from sparse coverage in English, correspondents say.
Communist Party mouthpiece Global Times said in an English editorial that Mr Liu was "a victim led astray" by the West.
"The Chinese side has been focusing on Liu's treatment, but some Western forces are always attempting to steer the issue in a political direction, hyping the treatment as a 'human rights' issue," the newspaper added.
Online in China, many comments on his death on social media appear to have been censored.
'Even RIP is being deleted by censors'
Liu Xiaobo memorialised in social art
Love that survived a labour camp
Mr Liu's friends in China have been told by authorities not to organise any memorial events according to Germany-based activist Tienchi Martin-Liao, who told the BBC that "many have been detained already".
Outside of the mainland, Chinese activists have been openly mourning him.
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Монгол эхийг энд дарж уншина уу