Australia had all the momentum heading into the blockbuster Ashes series against England in less than three weeks -- but that suddenly changed when a tearful Tim Paine quit as captain on Friday.

Paine's bombshell announcement, prompted by an explicit text exchange with a female colleague, leaves Australia facing a leadership vacuum and takes the spotlight off an England team desperate to avoid discussing the cricket racism scandal raging in their homeland.

Just this week, Australian pundits were relishing the prospect of the Ashes, saying the country's cricket "suddenly feels alive, armed and dangerous again" after a stunning T20 World Cup win.

They now head into the Ashes at home without a captain who has redefined the role since his appointment in 2018, winning widespread praise for reforming a toxic team culture.

The choice for replacement skipper appears to rest between Steve Smith -- who was stripped of the armband after the Sandpaper-gate ball-tampering scandal -- and paceman Pat Cummins.

Cricket Australia said that Cummins, Paine's vice-captain, "looks set to become the first fast bowler to captain the Test side in 65 years".

But respected Indian cricket commentator Harsha Bhogle said Cummins' workload meant Smith would likely get the nod, despite his tainted record.

"I suspect Australia will have to go back to Steve Smith as captain," Bhogle tweeted.

"Pat Cummins would be a deserving candidate but as a large-hearted fast bowler who gives every spell everything he has, and plays all three formats, his workload will need to be managed."

Australian commentator Gerard Whateley said Paine's sudden, tearful departure would "sit extremely heavily over Australian cricket going into the Ashes".

"There will be a national sense of shock and trying to take it in and comprehend it, and then to forecast what happens next, it's extraordinarily difficult to take in," he told SEN radio.

England captain Joe Root faces his own issues, with calls for him to address the issue of racism in English cricket. The tourists are currently at a training camp in Queensland.

"Keep in mind England cricket is in a full-blown crisis at the moment with the racism scandal that has been unearthed and their captain is not untouched by that," Whateley said.

He was "stunned" at the revelations involving Paine.

"It runs completely counter to the manner in which Tim has always conducted himself in the public sphere -- he has been a tremendously dignified and respectful captain," he said.