Updated at 4:20 a.m. ET Monday
The number of people confirmed killed after a tsunami and earthquake in Indonesia rose dramatically to 844 on Monday, Indonesian authorities said.
Officials warned that the number of people killed could even reach into the thousands as rescuers reach more affected areas.
A 7.5 magnitude earthquake triggered an unexpected tsunami in the Indonesian island of Sulawesi Friday, leaving hospitals and rescuers struggling to respond.
Most of the confirmed deaths are from the city of Palu. But rescuers worry that they could find more victims of the disaster in the Donggala region, which is closer to the epicenter of the earthquake.
Indonesian disaster agency spokesman Sutopo Purwo Nugroho said earlier that bodies of some victims were found trapped under the rubble of collapsed buildings, adding that hundreds more were injured and many were missing, according to Reuters.
Authorities said that "tens to hundreds" of people were by the ocean in the hard-hit city Palu for a beach festival when the tsunami struck on Friday just after 5:02 PM Western Indonesian Time.
"The tsunami didn't come by itself, it dragged cars, logs, houses, it hit everything on land," Nugroho told reporters.
Nugroho tweeted that Indonesia's military has been mobilized to assist search and rescue teams.
Yenni Suryani, Catholic Relief Services' country manager in Indonesia, said that this number "doesn't yet account for anyone who might have been swept to sea by the tsunami."
"I'm worried about people who might have been washed away," she added.
Nugrogo tweeted photos of local hospitals that are overflowing with the injured. Many people are being treated in makeshift medical tents set up out on the streets.
Multiple attempts have been made to reach out to Palu's main hospital, but it appears that its telephone lines may be disconnected.
Dramatic videos show rising waves smashing into buildings and people running away in fear.
Other footage has shown the aftermath: destroyed buildings and body bags lying in the street.
Several mosques, a shopping mall and many houses have collapsed, according to the CRS. The impact is significant, but the scope of the destruction is unclear because communications are down and emergency teams have not reached all affected areas.
Palu's airport also suffered damages, its runway badly cracked from the quake.
The Jakarta Post reported that one of the air traffic controllers, Anthonius Gunawan Agung, 21, died after he jumped off the traffic control tower when the earthquake hit the area.
His colleagues had evacuated the tower when they felt the trembling, but he stayed behind to ensure that an airplane safely took off, Air Nav Indonesia, the agency that oversees aircraft navigation, said in a statement.
Nugroho said that the casualties and the damage could be greater along the coastline 190 miles north of Palu in Donggala.
Communications "were totally crippled with no information" from Donggala, he added. More than 600,000 people live in Donggala and Palu.
NPR's Anthony Kuhn tells our Newscast unit that this is the most serious quake to hit Indonesia since August, when a series of tremors killed hundreds on Lombok Island.