BANGKOK — Soaring over eastern Indonesia on Friday, Petra Mandagi exulted at the perfect conditions for a paragliding addict: azure skies, a sweet breeze and a picture postcard bay rippling below.

Even when a series of earthquakes began shaking the city of Palu on Friday afternoon after his paragliding competition had finished, Mr. Mandagi texted his wife in their hometown, Manado, and assured her that all was fine.

Less than an hour later, twin natural disasters — a 7.5 magnitude earthquake and a tsunami that unleashed an 18-foot wave — turned parts of Palu and the surrounding strip of coastline into a graveyard. As of Sunday evening, national disaster mitigation officials said that at least 832 people had been confirmed killed.

The death toll, which had more than doubled from Sunday morning, was expected to climb much higher still, with heavily populated areas outside the city still cut off from any assistance, and desperate search-and-rescue efforts continuing in the rubble of Palu, often with only rudimentary tools.