LOWELL, Mass. (WHDH) -- A woman died after her car plunged into the Concord River in Lowell, trapping her inside the upside down vehicle for about 90 minutes Monday morning.

The accident happened at Lawrence and Moore Street in Lowell just after 6 a.m. A witness said the woman was driving on Lawrence Road, heading toward Billerica, when the car crashed into the jersey barriers. The car then went over the median and hit the wrought-iron fence before flipping over into the river.

Tina Kierce, who was driving behind the car that crashed, stopped and immediately called for help. Kierce told 7News she couldn't hear if anybody was trying to get out or call for help. She said bystanders wanted to help the trapped woman but the situation was too dangerous.

“The car had just flipped. It must have bounced off the guard rail, through the bridge. There's a railing, a wrought-iron railing. It flipped over it, so the car was upside down or face down in the water. It was submerged within four minutes,” said Tina Kierce, a witness. “It was under water within about four minutes.”

The first firefighters to arrive went in with only life jackets, but the water was too cold. Dive teams had problems with the current.

“The current was really strong so every time they tried to get into the car, the current would take their legs and pin it to the top of the car,” said Dep. Chief John Dowling, Lowell Fire Department.

The car was eventually towed to shore. When crews finally got to victim, they found her wedged in the back seat. It was unclear if she had been wearing a seatbelt.

The victim was transported to Lowell General Hospital where she was pronounced dead.

The cause of the accident remains under investigation.