Cuba's revolutionary leader Castro died last week at age 90, prompting an outpouring of grief in Vietnam where officials hailed him as a communist brother and comrade.

The Cuban embassy in Hanoi has filled with flowers from mourners since his death.

On Sunday, state offices across the country flew black-ribboned flags at half-mast while authorities called on entertainment venues to suspend activities for the day.

But the national day of mourning - afforded in the past only to the most senior Vietnamese politicians or war heros - has not been universally welcomed.

"He is not Vietnamese. We owe him for his support, but a day of national mourning is a bit too much," 25-year-old office worker Nguyen Luu Huong told AFP.

"It's ridiculous," businessman Hoang Bau added. "I am sure many Vietnamese do not care about it."

Vietnam is an authoritarian state where people are cautious about speaking out in public against the government.

On social media, where many Vietnamese feel less constrained, disapproving comments abounded.

"There is no laws for the Communist Party to ask the nation to mourn a foreigner, whoever that person is," said activist Le Dung.

"I do not support this decision at all," he told AFP.

In contrast, state-run media was filled with supportive comments saying a day of mourning for Castro was appropriate given he was one of the earliest and most steadfast supporters of Ho Chi Minh's communist revolution in Vietnam.

"Fidel Castro has been very devoted to our Vietnam, so a day of national mourning for him is worthy," wrote reader Bui Ta Vinh on the website of Tuoi Tre newspaper.

Cuba and Vietnam maintained strong ties even after the collapse of the Soviet Union and the end of the Cold War, despite the 15,000 kilometres (9,300 miles) that separates the two countries.

Castro has been lionised in Vietnam after a landmark visit to a battlefield in Quang Tri province in 1973, just days after communist's forces drove American-backed soldiers from the territory.

Cuba has funded infrastructure projects in Vietnam and paid for post-war recovery efforts even as coffers drained back home under Castro's hardline communist economic policies.

Fidel Castro visited Vietnam two more times after his historic battlefield visit, in 1995 and 2003.

Vietnamese leaders have often travelled to Cuba, including President Tran Dai Quang who was the last head of state to see Castro before he died.

The last person in Vietnam to be nationally mourned was legendary war general Vo Nguyen Giap in 2013.

Agence France Presse - December 4, 2016