Championship contender Alexander Rossi took a sizeable bite out of Kiwi Scott Dixon's Indycars Championship lead at the latest race at Pocono, Pennsylvania.

The race was delayed after a massive shunt involving Robert Wickens, Ryan Hunter-Reay and others and there was significant concern over Wickens' health for a period before Indycars announced that the Canadian was awake and alert after the incident.

Rossi dominated the 200-lap race to take maximum points with Will Power finishing second while Dixon had to settle for third.

It means Rossi moved to within 29 points of the lead of the championship with three races to go, including the double points finish at Sonoma.

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"It was an exceptional day today," Rossi said. "We are trying [to hunt Dixon down and win the championship]. We are executing like we said we would need to do."

Dixon was happy to salvage a good race result having qualified in 13th.

"It was very tough," Dixon said. "We tried to go off-strategy and then we got caught behind Marco, who is really hard to pass.

"We did OK today on points but obviously took a big hit with Rossi."

A wild crash halted the race eight laps in, Wickens and Hunter-Reay made contact and spun out in spectacular scenes.

Wickens' car flew into the air and smashed into the high fence, firing debris all across the track. The Canadian driver was taken from his car and loaded into a medical helicopter and taken to a nearby hospital.

Medical workers calmly attended to Wickens, who was taken to an ambulance before he was transported to the helicopter. The impact of the wreck tore out a large section of fencing that IndyCar said would take at least one hour to repair. The race was red flagged and drivers were allowed out of their cars.

A delay of more than an hour took place as fixes were made to the track.

The series moves to St Louis next week.