Australian sprinter Caleb Ewan surged past defending Tour Down Under champion Daryl Impey to win the second stage and seize the overall race lead on Wednesday.

Ewan, a three-time stage winner in last year's Tour de France, mastered the uphill finish in Stirling to claim the 135.8-kilometre second stage -- the first to run through the fire-ravaged district of Adelaide Hills -- for his Belgium team Lotto Soudal.

South Africa's Impey, chasing a third straight TDU title for Mitchelton-Scott, hung on for second and was boosted by a six-second time bonus with Australia's Cofidis rider Nathan Haas third.

Ewan bided his time in landscape lined by charred trees as his former Mitchelton-Scott team ratcheted up the pace on the final climb and the Australian unleashed a perfectly timed sprint to take the win by several bike lengths.

Ewan swept to the top of the race general classification ahead of first stage winner Sam Bennett with Impey one second behind in third.

Ewen's win followed Tuesday's first stage disappointment when he was out of position in the closing stages and came in a disappointing seventh.

"Yesterday things really didn't go to plan, and I think we spoke for about an hour in the room about what we could do, what we could do better," Ewan said.

"The (Lotto Soudal) boys did an absolutely perfect job today. They did everything I asked for. They brought me to the line in perfect position."

Impey was pleased to have gained a six-second time bonus and second in the stage to bolster his title hopes.

"We walk away with six seconds and to come second that's a pleasing result, especially after all of the hard work the guys did at the end there," Impey said.

"I have nine seconds now, it's a nice gap over some of the climbers but there's still a lot of guys in the bike race."

Irishman Bennett (Deceuninck-QuickStep) was near the front when the sprint cranked up in Wednesday's stage but faded out of the top 10.

The stage, which went through some of the areas badly affected by the recent bushfires where properties were destroyed and a person was killed, was marred by a crash in the final two kilometres that took down Elia Viviani (Cofidis), Simon Yates (Mitchelton-Scott) and Richie Porte (Trek-Segafredo), among others.

"I banged my knee a bit, but all okay," Porte said of the pile-up.

"The guys were awesome, really impressive today, and that bids well for tomorrow. I am really happy to see where we're at and riding so well as a team."

Viviani could be seen with large patches of road rash, but was walking around after the finish, while Yates was reported to have taken a heavy knock to his left knee and will be assessed before a decision on whether he continues in the race.

American Joey Rosskopf (CCC Team) claimed all the King of the Mountain climbing points to lead that classification.