Police believe fires at three caravans in the city centre were started deliberately.
Firefighters rushed to Dantzic Street on Sunday night to respond to the blaze.
No-one was hurt, GMP said.
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Officers have not made any arrests, and anyone with information is being asked to come forward.
Firefighters spent about two hours putting out the fires.
Detective Inspector Tim Berry, of GMP's City of Manchester district, said: "This incident could have escalated into something much more serious and we would like to speak to anyone who witnessed it or who has information that could help our investigation."
A GMP statement read: "Just after 8pm on Sunday 3 October, police and fire were called to a site on Dantzic Street in Manchester city centre to a report that three caravans were on fire.
"It is believed the fires were started deliberately and an investigation is under way.
"No arrests have been made and no-one was injured in the incident."
On Sunday, a spokesperson for Greater Manchester Fire & Rescue Service (GMFRS) said: "Just after 7.45pm today, four fire engines from Manchester Central, Philips Park and Salford were called to reports of three domestic caravans on fire on Dantzic Street, Manchester.
"Firefighters used breathing apparatus and two hose reels, as well as a ground monitor and a hose reel jet, to extinguish the fires before cooling and making the scene safe alongside our colleagues at Greater Manchester Police.
"GMFRS were at the scene for just over two hours."
Anyone with information is asked to contact 101 quoting log 2868 of the 3rd October 2021, use GMP's Live Chat function or report anonymously to Crimestoppers on 0800 555 111.
