Reigning series champion Will Power and defending race champion Scott McLaughlin have both copped avoidable contact penalties amid a crash-marred start to the Indycar season in Florida.

Australian veteran Power emerged with a seventh placing while his Kiwi teammate McLaughlin had to settle for 13th after contact with pole-starter Romain Grosjean while dicing for the lead.

Sweden's Marcus Ericsson outlasted the carnage on the downtown streets of St Petersburg on Sunday for a surprise victory for Chip Ganassi Racing.

It was supposed to be an Andretti car in victory lane, at least based on the speed the team showed all weekend. Their drivers Grosjean and Colton Herta started on the front row, but things began to unravel right at the start.

A seven-car accident on the first lap knocked five cars out of the race, including Andretti driver Devlin DeFrancesco, who was sent airborne when rookie Ben Pedersen slammed directly into his stopped car.

Helio Castroneves limped away from the accident while his Meyer Shank Racing teammate Simon Pagenaud clutched his hand.

Jack Harvey was transported to a hospital - IndyCar said it was for an evaluation out of "an abundance of caution" - after Kyle Kirkwood became the second Andretti driver to go airborne and sailed directly over Harvey's head.

Rinus VeeKay had slid into a tire barrier, Harvey ran into the back of VeeKay and Kirkwood launched over both cars.

But there was more to come.

Herta was sent into a tire barrier by contact from Power, who received his avoidable contact penalty, to leave Grosjean as the last remaining chance for Andretti.

But as Grosjean and McLaughlin raced side by side for position, the two cars touched in what appeared to be a game of chicken headed into a corner. Neither driver lifted and both cars slam into a tire barrier.

Grosjean was furious, first throwing his arms up in disgust, and then pounding his first on the stack of tires as he screamed. McLaughlin received his avoidable contact penalty.

Ericsson, meanwhile, passed Pato O'Ward for the win with three laps remaining when O'Ward suffered a brief loss of power and sailed on for the win for Honda.

"I think people forget us in some conversations when they talk about the championship," Ericsson said. "We're here to win. We won the (Indianapolis) 500. We were leading the championship for a long time. We're here to win."

O'Ward was second in a Chevrolet for McLaren and followed by six-time IndyCar champion Scott Dixon of Ganassi and Alexander Rossi in his debut race with new team McLaren.

McLaughlin and Power said they'd seek out Grosjean and Herta, respectively, to apologise, and McLaughlin went to Grosjean's team truck and hugged him.

with AAP