A mysterious green unidentified flying object or UFO in Jeffreys Bay had put rescue officials on alert on Monday night.

According to reports, the troubling incident occurred at around 9:30 p.m., and was immediately reported to the Traffic Control in Port Elizabeth.

Herald Live said the port quickly asked the National Sea Rescue Institute (NSRI) to investigate and monitor the area. The news outlet quoted spokesman Craig Lambinon who said:

"A Boeing 737 cargo aircraft Captain and Co-Pilot, flying from Cape Town International Airport to Port Elizabeth International Airport, reported seeing what appeared to be a green object increasing in altitude past the cockpit of their aeroplane reaching to about a thousand feet into clouds above them and then returning towards earth at high speed past the cockpit of the aeroplane."

"NSRI Jeffreys Bay were alerted and although the matter was monitored throughout the night the green object has not been seen since and there are no reports of anyone, or craft or aircraft overdue or missing," Lambinon added.

News24 reported that the object was estimated to be 1,000 feet (about 300 meters) above a plane before it completely vanished.

Just last month, another green orb was spotted in Japan. Express said that it has left some trails of light while it hovered above the skies of Niigata. A NIPPON TV subsidiary weather camera located in the eastern part of Japan was able to film the object.

While some UFO hunters claim that it's an alien spacecraft, astronomers had found a logical explanation for the green orb.

Speaking to NBC, an unnamed astronomer said it is called a "fireball" and the unusual luminosity is caused by space debris burning up as it reentered the atmosphere.

By definition, American Meteor Society said a fireball is another term for a very bright meteor, and is brighter than the light that planet Venus emits in the morning or evening sky.