* Massive waves swept many to their death
* Bodies found along shoreline
* Many collapsed buildings, 540 injured
* Death toll could be thousands - Vice President Kalla
* Disaster assessment hampered by cripplied communications (Adds speed of tsunami in paragraph 4.)
PALU, Indonesia, Sept 29 (Reuters) - At least 384 people were killed, many swept away as giant waves crashed onto beaches, when a major earthquake and tsunami hit the Indonesian island of Sulawesi, authorities said on Saturday.
Hundreds had gathered for a festival on the beach in the city of Palu on Friday when waves as high as six metres (18 feet) smashed onshore at dusk, sweeping many to their death and destroying anything in their path, following a 7.5 magnitude earthquake.
"When the (tsunami) threat arose yesterday, people were still doing their activities on the beach and did not immediately run and they became victims," Sutopo Purwo Nugroho, the spokesman for Indonesia's disaster mitigation agency BNPB said in a briefing in Jakarta.
"The tsunami didn't come by itself, it dragged cars, logs, houses, it hit everything on land," Nugroho said, adding that the tsunami had travelled across the open sea at speeds of 800 kph (497 mph) before striking the shoreline.
Some people climbed six metre trees to escape the tsunami and survived, he said.
Amateur footage shown by local TV stations showed waves crashing into houses along Palu's shoreline, scattering shipping containers and flooding into a mosque in the city.
Around 16,700 people were evacuating to 24 centres in Palu.
DEATH TOLL SEEN RISING
Aftershocks rocked the coastal city until Saturday afternoon following the massive earthquake on Friday, which triggered the tsunami. The series of earthquakes were felt in an area with 2.4 million people.
Nugroho described the damage as "extensive" and said thousands of houses, hospitals, shopping malls and hotels had collapsed. A bridge washed away and the main highway to Palu was cut off due to a landslide.
Bodies of some victims were found trapped under the rubble of collapsed buildings, he said, adding 540 people were injured and 29 were missing. Dozens of injured people were being treated in makeshift medical tents set up outdoors, TV images showed.
Photos confirmed by authorities showed bodies being lined up along the street on Saturday, some in bags and some with their faces covered with clothes.
Nugroho said the casualties and the damage could be greater along the coastline 300 km (190 miles) north of Palu, an area called Donggala, which is closer to the epicentre of the quake.
Communications "were totally crippled with no information" from Donggala, Nugroho said. More than 600,000 people live in Donggala and Palu.
"We're now getting limited communications about the destruction in Palu city, but we have heard nothing from Donggala and this is extremely worrying. There are more than 300,000 people living there," the Red Cross said in a statement, adding that its staff and volunteers were heading to the affected areas.
"This is already a tragedy, but it could get much worse," it said.
Vice President Jusuf Kalla said the death toll could rise to thousands.
PRESIDENT TO VISIT DISASTER AREA
Indonesia's meteorological and geophysics agency BMKG issued a tsunami warning after the quake, but lifted it 34 minutes later.
The agency on Saturday was widely criticised for not informing that a tsunami had hit Palu, though officials said waves had come within the time the warning was issued.
The quake and tsunami caused a major power outage that cut communications around Palu making it difficult for authorities to coordinate rescue efforts.
The military has started sending in cargo planes with aid, authorities said, from Jakarta and other cities, but evacuees still badly need food and other basic necessities.
The city's airport has been reopened only for relief efforts and will remain closed until Oct. 4 for commercial flights, Nugroho said. The airport's runway and air traffic control tower were damaged in the quake, authorities said.
President Joko Widodo is scheduled to visit evacuation centres in Palu on Sunday.
Indonesia sits on the Pacific Ring of Fire and is regularly hit by earthquakes.
In August, a series of major quakes killed over 500 people in the tourist island of Lombok and destroyed dozens of villages along its northern coast.
Palu was hit by tsunami in 1927 and 1968, according to BNPB.
(Reporting by Reuters stringer in PALU, Agustinus Beo Da Costa and Gayatri Suroyo, Fransiska Nangoy and Kanupriya Kapoor in JAKARTA Editing by Michael Perry and Neil Fullick)
Our Standards: The Thomson Reuters Trust Principles.