SOS Alarm and the Gothenburg air-rescue service were bombarded with telephone calls from mystified observers across southern and western Sweden shortly after 8pm on Saturday evening.
Witnesses reported seeing a huge flash of light stream across the night sky.
“There are a great many people who have seen it. We have received phone calls from Trelleborg to Lidköping,” said Annika Vestergård at the air-rescue service to news agency TT.
The light shone for only a couple of seconds but was enough to excite observes and prompt a raft of theories explaining the phenomenon.
Annika Vestergård said that one working theory is that the light was caused by a bolid, a meteorite that burns up in the atmosphere.
This theory is supported by Clas Svahn, chairman of the organisation UFO Sweden.
“This happens around ten times per year in Scandinavia and is therefore quite unusual,” he said to Sydvenska Dagbladet.
A further theory is that the flash of light was caused by a fragment of a satellite.
According to Swedish meteorological agency SMHI there were no weather phenomena that could explain the occurrence.