The rising Bakers Creek tide pushed against Fraser Lewis's sinking gut feeling the man trapped inside a truck partially submerged in the water could not have survived.

Standing on a disappearing sandbank, Mr Lewis and a crowd of bystanders were at a loss about what to do.

He had watched the oncoming truck crash off Bakers Creek bridge on the Bruce Highway about 5.20am Sunday.

The smoking truck cabin and seeping diesel indicated danger and having witnessed the truck plummet 10m below, hope felt lost.

But then, an anguished moan for help; a stronger, louder cry from the crushed cab.

"I was on my way to work at Daly Bay Coal Terminal," Mr Lewis said.

"The truck was coming towards me and we met on the bridge."

>>MORE: Bystanders pull driver from truck in Bakers Creek

The oncoming B-double veered sharply and suddenly to the left, ploughing through the guard rail and into the water below.

"The whole truck flew over the edge, crashing down, kind of gracefully, actually," Mr Lewis said.

"I jumped out of the car and called emergency services."

The 27-year-old jumped over the guardrail himself and went straight for the truck, joined by another man Thomas, a backpacker who had been travelling behind the truck.

"I thought there's no way someone could have survived that," Mr Lewis said.

The pair swam over to the truck, noticing diesel seeping from the truck and the cloud of steam. The cabin was crumpled, and they retreated to the bank and were joined by more people.

Then, the air brake released and Mr Lewis knew there was someone moving inside the cab.

"The passenger side was submerged and pretty banged up," he said.

"The tide was racing in as we were swimming over.

"We swam across and cracked the door, not knowing what (was inside)."

The 33-year-old truck driver was trapped inside "dangling by his seatbelt" with the water lapping his ankles.

"It could have been a lot worse," Mr Lewis said.

"He was reaching out for help. We manoeuvred him out and got him back to the bank."

Paramedics including critical care assessed him at the scene and the driver was later taken to Mackay Base Hospital.

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He suffered head and chest injuries and was in a stable condition Sunday afternoon.

Mr Lewis described the moment the truck flew over the guardrail like something out of a movie.

"It's like watching trains going off the tracks in movies," he said.

"Graceful. Straight through that guardrail."

Mr Lewis said he believed the truck could have blown a steer tyre as he recalled seeing sparks just moments before the heavy vehicle went over.

Bakers Creek bridge on the Bruce Highway was undergoing structural assessment before it could re-open to traffic.