Police arrested four people - a woman and three men - for loan-sharking activities on Thursday.

The woman, 33, was arrested near Queenstown by police officers on suspicion of helping loan sharks to harass debtors by locking their gates with bicycle locks and leaving notes outside their homes. She was also found with pieces of paper with writing relating to loan-sharking activities.

The three men - aged 35, 36 and 56 - were arrested by police officers at Eunos Road, Prinsep Street and Hougang Avenue 9.

Going by initial investigations, the three suspects are believed to have been involved in more than 20 cases of loan shark harassment at housing estates in many parts of Singapore, including Woodlands, Toa Payoh and North Bridge Road.

The activities included splashing paint and scrawling graffiti on the walls of Housing Board blocks with messages relating to loan sharks.

The 35-year-old suspect was found with two cans of spray paint, surgical masks and two markers.

The four suspects are expected to be charged on Saturday for loan-shark harassment.

First-time offenders will be jailed for up to five years, fined between $5,000 and $50,000, and get between three to six strokes of the cane.