INDIANAPOLIS -- Pole sitter Scott Dixon was knocked out of the Indianapolis 500 on Sunday by a terrifying crash that saw his car fly over the car of Jay Howard and land atop the inside safety fence, where it split in two amid sparks and flames.

Dixon's car was shredded by the retaining wall , but the tub of the car remained intact and the 2008 champion was able to climb out on his own to a roar from the crowd. He walked to a waiting ambulance while the race was placed under red flag and crews began to clean up debris scattered over hundreds of feet.

Howard also was checked at the infield car centre and released.

"Just a little beaten up there. It was definitely a rough ride," Dixon said. "I'm just bummed for the team, man. We had a great shot. We had gotten a little loose but they had dialed it in."

It's been a rollercoaster trip to Indianapolis for Dixon, a New Zealander who turned the fastest qualifying laps since 1996 to land on the pole. But that same night, Dixon was waiting in a drive-thru line at a nearby Taco Bell with three-time winner Dario Franchitti when he was held up at gunpoint.

Little did he know it wouldn't be his only frightening incident of the week.

Howard blamed the incident on Ryan Hunter-Reay. He'd run out of fuel earlier in the race and was already a couple of laps down when Hunter-Reay tried to get around him. Howard said that forced him to the top of the track, and the British driver for Schmidt Peterson Motorsports wound up in the outside wall.

That impact sent Howard across the track, where Dixon had nowhere to go.

"We were just out there trying to pick up some laps and Hunter-Reay got a run on me," Howard said. "I lifted, trying to be a nice guy. He comes right over on me and the rest is happy."

Dixon's car went airborne and flipped over before landing on the retaining barrier, where the impact punched a hole in the safety fencing. A photographer who was positioned at that point on the track ducked just in time as the car came apart; he was checked by safety crews and was OK.

Helio Castroneves was following them and barely escaped the carnage.

"It's tough," Dixon said. "You make those decisions, which way to go. You're hoping Jay is going to stay against the wall. I already had picked that way to go. There was nowhere else to go to avoid him. It's just a wild ride. You hold on and believe in the safety progress we've made."

Howard was making only his 13th career IndyCar start and his first since 2011, and that led Dixon team owner Chip Ganassi to question the series' eligibility rules.

The spectacular crash followed an incident involving Sebastien Bourdais during qualifying weekend, when he wiggled twice going through the same corner and hit the wall. The tub of his car collapsed and Bourdais was left with a fractured pelvis, hip and ribs.

Bourdais, who was at the track Sunday, joined Franchitti in visiting Dixon at the care centre.

Dixon was among the heavy favourites to win his second Indianapolis 500 this weekend. He had been fast through practice before landing on the pole, and his Honda-powered ride had him near the front of the field when the crash occurred on Lap 54.

"It was," Dixon said, "a wild ride."