A 170-foot crane cracked and tumbled to the ground last night, killing a workman and injuring four others. The upper section of the crane broke off during work in midtown on the extension of the No. 7 subway line. It crashed "like a dinosaur," a construction site worker told the New York Times. Investigators are "looking at some kind of failure in the rear of the crane," a source told the Times. A 30-year-old worker was killed. Those hurt were a crane operator, a flag man, a relative of one of the victims, and another man. Some were saved from 60 feet below ground, and ropes were used to lift people out. "It was a complicated job," said Fire Chief William Seelig. The rescue scene was a "very precarious area with a lot of construction material." (More Manhattan stories.)