MELBOURNE - Bushfire victims had no hope of anticipating the catastrophe of Black Saturday because warnings on the day were insufficient, the royal commission into Victoria's bushfires has heard.

The commission is in its first official day of business, with a directions hearing being held in the Victorian County Court.

The fire was too fast and too intense for people to reasonably decide whether to stay or go, the court was told.

In his opening address, counsel assisting the bushfires royal commission, Jack Rush, QC, said the inquiry would firstly examine the bushfire warning system and stay or go policy.

But he said any recommendations on the policy would not be complete in time for the interim report in August or next summer's bushfire season.

Mr Rush said the evidence would suggest that timely information was not available to warn people on the day.

"People remained in their homes unaware of the approaching fires until it was too late," he told the court.

Others stayed, unaware of the intensity of the fires they would face, he said.

The Black Saturday fires could "not be imagined by our generation".

"It's speed was phenomenal," he said.

Mr Rush said the evidence to the royal commission would show people's decisions to stay or go were "unrealistic" due to the extreme fire conditions on February 7.

He said the only warning on the day was for an extreme fire danger.

"Such general warnings (are) not a trigger to go early."

Mr Rush said unlike other countries Australia allowed people to make a choice about whether to stay or go rather than evacuate.

"In other countries with a high bushfire risk evacuation is still seen as the safest emergency approach," he said.