The US Geological Survey (USGS) said on Tuesday that the quake occurred at 2:08 p.m. local time about 100 kilometers southeast of Kupang, the capital of East Nusa province, at a depth of 10 kilometers with the epicenter in the sea.
There have been no tsunami warnings or immediate reports on the damage or possible casualties, Presstv reported.
Spokeswoman of the Kupang district administration Martha Magdalena Para Ede said the jolt had been so strong that "in panic we rushed out of working office for safety."
Earlier in August, a succession of earthquakes hit the Indonesian island of Lombok east of Bali, leaving over 550 people dead.
"I was on the second floor of my office and suddenly everybody ran outside because of the earthquake," an AFP reporter in Kupang said. "All the chairs were shaking ... we were traumatized by all the earthquakes in Lombok."
Some hours before the quake in Kupang, a shallow 4.7-magnitude tremor hit the north side of the Timor Island in Indonesia.
Indonesia is one of the quake-prone countries lying on the Ring of Fire, where many of the word’s earthquakes and volcanic eruptions occur.