The initial quake sparked a tsunami with waves of up to two metres high destroying buildings and washing ships aboard close to the city on the Indonesian island of Sulawesi, with multiple deaths among the 600,000 residents highly likely.
According to the US Geological Survey (USGS) the huge quake triggered a further 23 others, the majority of which are in the Pacific Ocean and within 10km of the main quake’s epicentre.
The largest of these are two 5.8-magnitude tremors located 21km south east of Palu and 99km north of the city, sending huge waves of water crashing onto the island from all directions.
Three other quakes have increased the scale of the disaster in terms of distance and acceleration of ocean water.
These are 154.4km south east near the Barat Daya Islands (4.5 magnitude), 4.5km south east of Sinabung (4.6 magnitude) and 194km west of Matthew Island and Hunter Island in the South Pacific (4.9 magnitude).
The huge 7.5 magnitude earthquake hit as dusk fell on the island, initially bringing down communications and forcing the closure of the airport.
In a live TV interview, Indonesian disaster agency spokesman Sutopo Purwo Nugroh said the resulting tsunami had swept away homes, with many families reported missing.
He added search and rescue efforts are being hindered by the darkness, with several communications lines down on the island.
The national search and rescue agency is deploying a large ship and helicopters to help with the operation.
Dwikorita Karnawati, who heads Indonesia’s meteorology and geophysics agency, BMKG, said: “The 1.5- to two-metre tsunami has receded.
«It ended. The situation is chaotic.
«People are running on the streets and buildings collapsed. There is a ship washed ashore.»
Indonesia is a particular hotspot for earthquakes as it is located on the Ring of Fire, a 40,000km area in the Pacific Ocean.
This is where many of the world’s natural disasters occur due to it sitting on top of continuously sliding tectonic plates.
The country has been struck by a series of earthquakes over the past two months.
Nearly 500 people were killed in July and August alone on the holiday island of Lombok — hundreds of kilometres southwest of Sulawesi.
According to Indonesia’s disaster agency, nearly 400,000 people remain displaced after the disaster.
Reconstruction efforts are now underway on the island, with the quakess causing £263 million ($340 million) in damage.
In 2004, an earthquake off the the northern Indonesian island of Sumatra triggered a massive tsunami across the Indian Ocean, killing 226,000 people in 13 countries, including 120,000 in Indonesia.
Palu, famed for its long sandy beaches and water sports, was hit by a 6.2 magnitude earthquake in 2005, which killed one person.