An insider from Zimbabwe's ruling government has posted information suggesting that longtime president of the African nation Robert Mugabe has collapsed.

Happyton Bonyongwe, the Director-General of the Zimbabwean Central Intelligence Organisation, has reportedly tightened security at State House in Zimbabwe, a day after fears for Mugabe's health surfaced, according to internet commenter Baba Jukwa.

Baba Jukwa, an insider in the ruling Zanu-PF party who uses a Facebook page to expose corruption in the regime, on Saturday reported rumours that Mr Mugabe had collapsed.

However, he added that Mr Mugabe's press secretary, George Charamba, had denied that the President was ill.

There have been rumours for several years that Mugabe, who turns 90 next month, has prostate cancer.

Baba Jukwa, who calls himself "a disgrunteld Zanu-PF insider", said on Saturday that Mr Mugabe had "gone on his final visit" to his doctor. Mr Mugabe had previously offered a $US300,000 reward for the unmasking of Baba Jukwa.

Baba Jukwa has successfully exposed corruption in Zimbabwe in the past, and last year he warned that Edward Chininga, a former Zanu-PF member of parliament who had been critical of Mugabe, would die soon.

Weeks later, Chininga died in car accident. Staged road accidents are a common form of assassination in Zimbabwe.

In his latest post, Baba Jukwa says that security has been tightened at State House but there is no information on Mugabe.

"If it is true that he has died, they are likely to keep his body refrigerated until security chiefs pass the nod to announce," Baba Jukwa said.

"When that will be? It could even be 6 months later. This is the way to do it in line with protocol.

"Meanwhile Pray for your country Great Zimbabweans so that there is no bloodshed."