Hong Kong police have arrested 12 people in a six-day crackdown on illegal debt collection gangs accused of splashing red paint on buildings and making threatening phone calls over outstanding loan payments.

Inspector Lam Kin-yu of the Wong Tai Sin anti-triad squad said the suspects were detained in a series of raids between Friday last week and Wednesday.

They were linked to 18 debt-related criminal damage and intimidation cases in Wong Tai Sin and Sai Kung, involving HK$5.4 million…