A sanitation worker died in a horrific accident Saturday after he was struck and pinned by a street sweeper in Queens, police said.

Stephen Frosch, 43, had been working on his own street sweeper when he was fatally struck by another one at a Department of Sanitation garage in Bayside at around 1 p.m., officials said.

“The worker was pinned by another mechanical sweeper that did not see him,” a department spokesman said. “A complete investigation is under way.”

Paramedics rushed to the heavily industrial neighborhood but ­Frosch, of Garden City, LI, was pronounced dead at the scene.

He had been with the department since 1999. He had a wife and four children.