PANAJI, India — Rescuers using backhoes and shovels searched for survivors on Sunday under a huge pile of broken concrete after a residential building under construction collapsed in southern India, killing at least 15 workers.

The authorities said they suspected that dozens more might be trapped under the rubble, but they were still trying to determine how many workers were at the site when the five-story structure crumpled Saturday afternoon in the state of Goa. Witnesses reported seeing at least 40 workers.

Soldiers and firefighters listened for movement or cries from the wreckage as they worked overnight to clear the debris, said a state official, Venancio Furtado.

At least 10 people were pulled out alive overnight, but the chance of finding survivors was dwindling, Mr. Furtado said. By Sunday afternoon, the death toll had reached 15, according to the state government.