A mysterious monolith has appeared in the Nevada desert over the weekend, sparking speculation as to what it may be and who is behind it.

The structure was spotted by the Las Vegas Police Department, who said they saw it during a search and rescue mission north of the Las Vegas Valley.

“We see a lot of weird things … but check this out!” the police posted on social media.

The monolith is similar to other similarly puzzling ones that appeared around the globe in 2020.

The tall, rectangular, reflective structure was spotted near Gass Peak, a hiking area in the Nevada desert just about an hour north of Las Vegas.

In pictures released by police on social media, the monolith appeared to be nestled in slightly rugged terrain.

“HOW did it get up there??” the Las Vegas Police Department asked on social media.

The monolith bears some resemblance to those featured in 2001: A Space Odyssey, a 1968 film directed by Stanley Kubrick.

Imposing black monoliths created by an unseen alien species appear in the classic movie, which is based on the writing of novelist Arthur C Clarke.

Monoliths similar to the one in Nevada appeared in different locations around the world about four years ago, including one in the Utah desert.

That one left local authorities baffled after it was discovered by a helicopter pilot flying overhead in November 2020.

Another one was found in Romania around the same time, as was one in California and on the Isle of Wight in the English Channel.

Speculation brewed then as to who may be behind them, with some wondering if they were part of an art installation. But no one has come forward since to claim they were behind the structures.

Another monolith more recently appeared on a hilltop in Wales in March. Observers said the sculpture looked perfectly level, but it offered no clues as to who could have placed it there.

While the mystery behind the monoliths remains, Las Vegas authorities used their latest discovery to remind people hiking in the Nevada desert to be prepared for the hot weather and to stay safe.