"This caused an underwater landslide and eventually caused the tsunami", said Dwikorita Karnawati, head of the meteorological agency, adding that the waves hit shorelines 24 minutes later.
The spokesman for the National Disaster Mitigation Agency (BNPB), Sutopo Purwo Nugroho, who has become a reliable source for the series of disasters that have hit Indonesia, announced shortly after midnight on Sunday that tidal waves had swamped beaches in Lampung province on the southern tip of Sumatra and in Banten on the western coast of Java.
The nation of islands has a network of tsunami-detecting buoys - devices floating off the country's coasts created to submit warnings about big waves to its national disaster agency - but they have been broken since 2012, an agency spokesman said.
"I heard people shouting to run away and I saw the water had gone up to the mainland and the hotel had been flooded by water", said witness Feri Ardian.
As of December 24, Trudeau has not elaborated on the type of aid the government plans to send, nor offered a timeline for deploying it. Debris from thatch-bamboo shacks was strewn along beaches. "They need to be rebuilt to strengthen the Indonesian tsunami early warning system", he advised.
Many of those affected were domestic tourists enjoying the long holiday weekend, but foreigners were visiting the area ahead of Christmas as well.
Sutupo said there was no tsunami advance warning system on the night of the latest disaster.
In July, the Anak Krakatau volcano put on one of its most violent displays, spewing "lava bombs" as big as trucks.
Coastal residents barely had time to register the waves of 1-3 meters (3-10 feet) before the wall of water slammed into them.
It erupted again just after 9 p.m. on Saturday and the tsunami struck at around 9:30 p.m., according to Indonesia's Meteorology, Climatology and Geophysics Agency, BMKG.
Tsunami survivors gather at temporary shelter in Tanjung Lesung, Indonesia, Dec. 23, 2018.
Among the victims were members of the Indonesian rock band called Seventeen, who were performing on stage as the tsunami hit.
The volcano's name translates to "Child of Krakatau", a volcanic island formed in 1920 after one of the largest, most devastating eruptions in recorded history occurred at the Krakatau volcano in 1883, which sent ash clouds that encircled the globe.
The death toll from a tsunami on the Indonesian islands of Java and Sumatra jumped to at least 373 as rescue workers stepped up efforts to reach many areas swept away by the deadly waves.
Jaw dropping footage of the exact moment the 20ft wave came crashing down on the stage, engulfing the band, emerged on Sunday morning as it was revealed 220 are dead.
"The likelihood of further tsunamis in the Sunda Strait will remain high while Anak Krakatoa volcano is going through its current active phase because that might trigger further submarine landslides", he said.
The tsunami struck Indonesia's two most populous islands.
Indonesia is prone to tsunamis because it lies on the Ring of Fire - the line of frequent earthquakes and volcanic eruptions that circles virtually the entire Pacific Rim.
Indonesia has been hit by a series of natural disasters in recent months, including a powerful quake that hit the island of Sulawesi on September 28.