Two houses on Rectory Road were cordoned off by police
Detectives are to continue questioning three men arrested on the M65 in Lancashire in a counter-terrorism operation.
Searches are also underway at five properties in Burnley
Three vehicles also seized on Friday night were to join a convoy taking £1m in aid to Gaza.
Nine men were originally arrested but six were later released. The remaining three in custody are aged 26, 29 and 36, police said.
The arrests were carried out as part of a joint operation by Lancashire Constabulary and the North West Counter Terrorism Unit.
The houses being searched are understood to be on Gordon Street, Robinson Street and Clive Street, with the other two on Rectory Road.
Ch Supt Neil Smith, divisional commander for Pennine Division, said officers were "working hard to ensure everyone is kept up to date with as much information as we can give".
"We will endeavour to carry out any searches as quickly as possible to minimise the impact on the area concerned," he said.
Meanwhile a Lancashire Constabulary spokeswoman said the cargo from the seized vehicles was being thoroughly checked.
She said search officers were "working as quickly as they can to ensure that the parcels can be released and continue on to their destination".
More than 100 vehicles are taking aid such as medicines, tools, clothes and blankets to Gaza.