A cyclist was critically injured — with her arm nearly severed — when she was struck by a hit-and-run city sanitation truck in Brooklyn on Wednesday night, cops said.

The 25-year-old woman was pedaling in the bike lane on Evergreen Avenue near Grove Street in Bushwick at about 8:30 p.m. when the garbage truck struck her and continued driving, police said.

Cops caught up with the driver nearly two miles away at Varick Avenue and Mesorole Street, police sources said.

The driver was being questioned by cops as of early Thursday.

Police were looking to determine whether the city worker even knew he had struck the woman.

The cyclist was taken to Brookdale Hospital in critical condition, authorities said.

A witness said the woman’s left arm was nearly severed.

“Half her arm was hanging off. It was awful,” the witness said. “She was just laying in the bike lane, not really moving.”