SAN FRANCISCO (CBS/SF) – Two portable toilets were set on fire within minutes of each other in San Francisco’s Castro District early Sunday morning, a crime that has occurred dozens of times in recent years.

Officers responded to two separate reports of toilets on fire shortly after 12:30 a.m. Sunday. One of the fires was at 18th and Sanchez streets, and the other was several blocks away at 18th and Douglass streets, according to police.

READ MORE: COVID Vaccine: San Francisco Opens Eligibility to All Residents Age 16 and Up

The portable toilets were both outside homes under construction, and in each case, half of the backside of the toilet was melted by the flames, police said.

Arson is suspected in both fires, but no suspects have been identified, according to police.

READ MORE: UPDATE: Paul Flores, Suspect In Cal Poly Student Kristin Smart's 1996 Disappearance Arrested

The city was plagued by dozens of apparent arson cases at portable toilets in 2009. Police had reported fewer incidents in recent months.

Anyone with information about the blazes is encouraged to call the Police Department’s anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.

MORE NEWS: COVID: 4/20 Celebration At Hippie Hill In Golden Gate Park Canceled For 2nd Year In A Row

(Copyright 2011 by CBSSan Francisco. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. Wire services may have contributed to this report.)