Humberside Police are investigating three suspected arson attacks within half an hour in the East Marsh area of Grimsby.
Officers believe fires were deliberately started when items of refuse were set alight close to properties on Victor Street, Stanage Walk and Tom Hammond Way between 9.30pm and 10pm on Tuesday, December 12.
No-one was injured and all the fires were safely extinguished.
One of the properties had to be evacuated as a precaution.
Detective Chief Inspector Nicki Miller of Humberside Police said: “Our officers quickly responded to these incidents along with our colleagues from Humberside Fire and Rescue, and enquiries started immediately.
“We would like to reassure the local community that we are actively continuing those enquiries.
“We have an increased presence in the area and we are pursuing a number of lines of enquiry to identify who is responsible for these incidents.
“We have been undertaking house to house enquiries as well as studying CCTV.
“We are determined to find out how the fires started and to deal with anyone involved in these incidents to make sure we keep our communities safe.
“If you know anything about these incidents please call us on 101 quoting log 473 of 12 December 2017. Calls can also be made anonymously to Crimestoppers on 0800 555 111.”