Firefighters worked to rescue a worker trapped for hours beneath the rubble of a medieval tower that partially collapsed while under renovation in the heart of Italy's capital on Monday, critically injuring another worker.

Firefighters faced a complex task as the structure continued to give way as they tried to get near the trapped worker through a first-floor window, forcing their retreat on telescopic aerial ladders in a cloud of smoke.

Another approach on two ladders was also aborted, and a drone sent up in their stead.

As dusk approached, firefighters lifted on a crane used giant tubes to suck rubble out of the second-floor window.

Three workers were rescued unharmed after the initial midday collapse, said firefighter spokesperson Luca Cari.

Italian media reported that another worker, age 64, was hospitalized in critical condition but there was no immediate update on his condition.

No firefighters were injured in the ongoing operation.

Rome's top law enforcement official, Prefect Lamberto Giannini, said there were “signs of life” from the trapped worker, and that firefighters had managed to give him some protective cover during an earlier rescue attempt.

Giannini called the situation “very complex” and said that other equipment was being brought in.

Hundreds of tourists had assembled to watch as firefighters used a mobile ladder to bring a stretcher to the upper level of the Torre dei Conti during the first rescue attempt.

Suddenly, another part of the structure partially collapsed, sending up a cloud of debris and forcing firefighters to quickly descend on the ladder.

The Torre dei Conti was built in the 13th century by Pope Innocent III as a residence for his family.

The tower was damaged in a 1349 earthquake and suffered subsequent collapses in the 17th century.

Rome Mayor Roberto Gualtieri and Italian Culture Minister Alessandro Giuli were at the scene, but did not speak to reporters.

“The firefighters risked their lives with the second collapse. We are worried for the worker who remains trapped,'' said Federico Mollicone, chairman of the parliamentary culture committee.

AP video shot by: Silvia Stellacci