Prime Minister Tony Abbott came under criticism last week from the public and Labor MPs for not lowering the flag on the day of Mandela's death.

The Department of Prime Minister and Cabinet said the flag would only be lowered for the funeral of a serving head of state of another country with which Australia has diplomatic relations, but not for the funeral of a former leader.

Deputy opposition leader Tanya Plibersek joined social media users in criticising the decision, taking to micro blogging platform Twitter to call for the flag to be lowered.

The hashtag #lowertheflag was used more than 9,500 times and trended in Australia on Friday.

On Saturday Prime Minister Tony Abbott announced all Australian Government flags would be flown at half-mast on Tuesday, the day of the official memorial at the FNB Stadium in Johannesburg.

The Department of Prime Minister and Cabinet issues Commonwealth Flag Network Notices for federal government departments and agencies.

Recent notices have included state funerals for former state and federal ministers and last month's commemoration of Remembrance Day.

Many of Canberra's diplomatic missions lowered their flags on Friday, while flags were lowered at 10 Downing Street in London and the White House in Washington.

Traders at the New York Stock Exchange paused for a minute of silence on Friday and the city's historic Apollo Theater announced the death on its marquee.

The flag at Canberra's British High Commission was not changed on Friday.

Mr Abbott and Opposition Leader Bill Shorten are in South Africa for today's memorial service.

''We honour a truly great world leader, an extraordinary man and an honorary companion of the Order of Australia,'' Mr Abbott said.

On Tuesday a Department of Parliamentary Services spokeswoman said the flag had been lowered at 8am as a mark of mourning and respect and in accordance with protocol.

The Commonwealth Flag Network has instructed that the flag remain at half-mast all day Tuesday.