A powerful earthquake struck off the coast of Indonesia early on Saturday, killing at least 20 people and toppling buildings, authorities said.

At least two people were known to be trapped alive under rubble, rescue official Fathur Rahman told AFP news agency.

The epicenter of the magnitude 7.7 earthquake hit off the coast of the island of Flores at a shallow depth of 10 kilometers (6.2 miles), the US Geological Survey (USGS) said.

Shallow earthquakes (up to 70 kilometers deep) are considered more dangerous and destructive.

Tsunami waves of less than 1 meter (3 feet) were recorded in several areas of the country before the warning was lifted about three hours after the quake.

Where did the earthquake strike?

Indonesia's Meteorology, Climatology, and Geophysics Agency (BMKG) recorded the first quake at 4:58 am (2158 GMT) at a depth of 15 km (9 ⁠miles), followed by dozens of aftershocks.

Video shared on social media from Maumere, the main town in Sikka Regency on Flores Island in eastern Indonesia, showed part of a building collapsing in a cloud of dust and rubble as people screamed and ran into the street.

"Many buildings here were damaged ... I saw that the waiting room at the Pelni port terminal in Maumere had collapsed," Yohanna Embu, a resident of Sikka, a regency within East Nusa Tenggara province, told AP.

Residents evacuated, tsunami warning lifted

The initial jolt was followed by a series of aftershocks in the same area, including one of magnitude 6.1.

BMKG issued a tsunami warning for part of East Nusa Tenggara, West Nusa Tenggara, South Sulawesi and Southeast Sulawesi provinces, urging residents to stay away from beaches and riverbanks.

The tsunami warning was later lifted.

"We have ended (the tsunami warning) but we will keep monitoring the sea level," Wijayanto, earthquake and tsunami director at BMKG, said.

Before the tsunami warning was lifted, residents of Maumere on Flores Island were told to move to higher ground, according to AFP.

State television also showed hundreds of people evacuating in nearby Nagekeo regency.

Local TV footage showed a hospital in the district of Ende in East Nusa Tenggara Province moving patients outside.

Authorities assessing damage, casualties

The quake caused severe damage and collapsed buildings, causing power outages in cities and villages, severely hindering rescue operations.

"We are continuing to collect reports of damages and casualties, but there are communication disruptions," East Nusa Tenggara police chief Rudi Darmoko said.

Local television reports showed patients at several hospitals being evacuated from buildings as a precaution.

"Our students and nuns ran out in panic beneath a collapsing roof," Guidelbertus Tanga, rector of Ritapiret Seminary on Flores said. "At least one priest suffered a broken leg after jumping from the second floor of a building during the quake."

There were also damages reported in some part of southern Sulawesi island.

Indonesia's history of earthquakes

Indonesia is located on the so-called "Ring of Fire," a region of heightened seismic activity in the Pacific basin that stretches from Southeast Asia to Japan.

Here are some of the biggest earthquakes to strike the region:

• 1992, magnitude 7: A tsunami following a strong earthquake on the southeastern island of Flores killed about 2,500 people
• 2004, magnitude 9.1: A quake struck off the coast of Sumatra triggering a tsunami that killed 170,000 in Indonesia and 220,000 in several countries in the Indian Ocean
• 2018, magnitude 6.9: A tremor killed more than 550 people on the islands of Lombok and Sumbawa
• 2018, magnitude 7.5: A quake and a subsequent tsunami in Palu on Sulawesi island left more than 4,300 people dead or missing

Edited by: Karl Sexton

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