A US city has warned residents to be vigilant following a number of 'clown sightings'.

Police in Greenville in South Carolina say they have "answered four calls related to clowns" over the last week.

It follows a pair of other sightings in the wider Greenville County area last month.

Greenville City Police have revealed details of four separate reports, with two sightings apparently taking place near the same apartment complex.

In the first incident on Monday, a young man reported two clowns standing outside the complex - but officers were unable to find any evidence either at the location or on CCTV.

The next day, a similar report was made, with two people in clown costumes reportedly spotted near a playground near the apartment complex. They were apparently chased and escaped in a car.

In the third incident - which is said to have happened on Wednesday - a person dressed in black, wearing a clown mask, was apparently seen walking toward the back garden of a residence. 

Later that day, a woman reported that a man wearing "clown-like facial makeup and red hair" stared at her as she exited a laundry.

It has been speculated that the incidents could be 'viral marketing' for the horror film 31, directed by Rob Zombie.

However, WTVR reports that officers at a press conference said they do not know if that is the case.

Greenville Police say: "In each of the four Greenville City incidents, there has been no indication of any attempt to contact or lure children into the woods. In general, however, members of the community should remain vigilant.

"Don't allow children to play alone or in isolated areas; parents and guardians should be aware of their children's activities," the police statement adds.

The warning follows allegations that incidents outside the city involved 'clowns' attempting to lure children into the woods.