WASHINGTON (AFP) - It may just be brotherly love, but former president George W. Bush said Thursday that his younger sibling Jeb wants the White House in 2016 - and he's encouraging him to run.

"I think he wants to be president," George Bush told Fox News.

"I think (Jeb would) be a great president. He understands what it's like to be president."

Jeb Bush, a favourite among some establishment Republicans who believe he would be a prime opponent to an increasingly likely run by former secretary of state Hillary Clinton, has said he will decide next year.

"(Jeb) and I had a conversation. I of course was pushing for him to run for president, he of course was saying, 'I haven't made up my mind,'" the former commander-in-chief said.

But George Bush said there was plenty of family presidential precedent to turn to in helping make a decision.

"He's seen his dad (George H.W. Bush), he's seen his brother. And so he's a very thoughtful man, and he's weighing his options."

Jeb Bush, 61, is viewed as a mainstream Republican and less ideologically rigid than the conservatives considering a presidential run, like Senator Ted Cruz.

Jeb Bush, who served as Florida governor from 1999 to 2007, has notably expressed support for immigration reform, including the mass legalisation of undocumented workers.

A survey of Florida voters this month showed odds-on Democratic frontrunner Clinton ahead of all potential Republican rivals - including Bush and Florida native son Senator Marco Rubio - in a hypothetical 2016 race.

The Clinton-Bush matchup was closest at 46 per cent to 44 per cent, within the poll's margin of error.