Three people have been arrested and explosive experts were called to an incident at a property in Billingham, Stockton-on-Tees.
Police were called to a domestic incident on Collingwood Road at around 11pm on Saturday 16 September.
Following a search of the property, officers say they found a number of "suspicious" items.
Specialist officers and Explosive Ordnance Disposal (EOD) experts were called and currently remain at the scene whilst investigations continue.
Three people were arrested in connection with the incident, and they currently remain in police custody.
A police cordon remains in place and officers from Cleveland Police will be in the area throughout the course of the investigation.
Anyone with information should contact the force on 101, quoting reference number 186330.
Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To Know...