PLYMOUTH, Mass. -- Plymouth police were investigating the cause of an accident that sent an SUV crashing off the end of a pier on Water Street into Plymouth Harbor Wednesday night, injuring two young people inside.

Both victims, a male and a female, were pulled from the water unconscious. They were reported in critical condition at Boston Medical Center. No names were released, but both were said to be in their 20s.

A few witnesses watched in horror as the car plunged off the concrete dock.

"I saw two teenagers, a male and a female, come out from the dock, get into the car. The male put it in drive, probably went back, at the most, 5 feet. Put it in drive and at the same time floored the gas and then it just went over and lunged into the water," Justin Lane said.

Lane said he called 911 and then ran to the Jeep in the water, which was sinking nose down into the harbor water, which is about 16 feet deep in that area. He could see the female passenger struggling to escape.

"She was trying to kick out the front window. The male was just sitting there. Probably within five minutes it was under," Lane said.

His friend Lindsay Lyon also watched the terrible scene unfold.

"I was in complete shock. The first thing he did was call 911 and then we just ran over here and saw the girl, like he said, trying to kick the windshield out," she said.

Three divers worked to open the Jeep doors, but by the time they did, more than 30 minutes had passed. Both the driver and passenger appeared to be unconscious. Both were initially taken to Jordan Hospital, then flown to Boston.

Lane said he couldn't believe what happened right in front of him.

"I didn't hear any argument. No fighting, no nothing. My windows were down. But I don't feel that it was an accident," Lane said.

Investigators said they were looking into whether the car was driven off the end of the pier deliberately.