Residents in Nagekeo regency, the area closest to the epicentre, raced for higher ground as the sea retreated — a possible sign of an approaching tsunami, AFP journalists saw.
The warning was later lifted.
The epicentre of the shallow quake was located off the north coast of the island, about 68 kilometres (42 miles) northwest of the coastal town of Ende, US and Indonesian authorities said.
The initial jolt was followed by strong aftershocks in the same area, including one with a magnitude of 6.1.
“Suddenly it started to shake and I panicked,” 31-year-old hospital customer service official and Maumre resident, Lukas Lotar, told AFP.
“Patients also fled the hospital, the jolt was big. I saw some walls were cracked,” he said.
A resident in Nagekeo, Yohanes Babo, 56, said he was at a market when the earth started shaking.
“The shaking was strong. Thankfully, we were already outside the house,” he told AFP.
“People were panicking, running here and there. We’re evacuating for the time being… and trying to get to the hills,” he said, adding: “My family is safe. No one was harmed.”
Indonesia’s Meteorology, Climatology, and Geophysics Agency (BMKG) warned of the possibility of tsunami waves following the quake and urged people to get to higher ground.
“We strongly urge our communities along the northern coast of Flores and in the southern parts, on the southern islands and across the southern region, to carry out self-evacuation immediately,” Abdul Muhari, an official at the national disaster agency, BNPB, said.
Residents should “move away from the shore, either by going more than two kilometres inland or by moving up into hilly areas more than 10 meters high,” he told local broadcaster Kompas TV.
BMKG earthquake and tsunami director Wijayanto said tsunami modelling suggested the potential for a tsunami in the provinces of East Nusa Tenggara, South Sulawesi, and West Nusa Tenggara.
An alert was issued for waves ranging from 0.5 metres to three metres (1.6 to 9.8 feet), but was later lifted.
“We have ended (the tsunami warning) but we will keep monitoring the sea level,” said Wijayanto, who like many Indonesians, goes by one name.
Residents in the town of Maumere on Flores Island were evacuating to higher ground, an AFP correspondent saw.
Images broadcast on Indonesian television showed hundreds of people in nearby Nagekeo regency evacuating the area from among the rubble of damaged buildings.
Authorities have not reported any casualties, but said tsunami waves between 19 and 30 centimetres have been detected.