The number of juveniles under 15 who were arrested in the first half of this year surged nearly 40 per cent compared with the previous six months, police said yesterday. Social workers also noted a new trend of children as young as seven bullying younger schoolmates for as little as $10. Senior Assistant Police Commissioner Lau Chun-sing said the overall number of crimes in the first half of this year rose to 39,155 - 5.4 per cent higher than the same period last year. He said 3,477 young people aged seven to 15 were arrested in the first half of this year - 37 per cent more than in the previous six months and 20 per cent more than the same period last year. 'The increase in percentage is big, but the actual number is not big when compared with the population of young people in Hong Kong,' Mr Lau said. 'But the rise is an indicator to remind the police that it's an area that we have to pay attention to.' He said the arrests were mostly for thefts, shoplifting and assault. There was also a rise in robberies involving bullying. The supervisor of the Caritas Integrated Service for Young People (Wong Tai Sin), Charles Chan Chi-kwong, said: 'We noted during the past year that some Primary Five and Six students bullied their Primary Three and Four schoolmates for $10 or $20. When the victims did not have money to pay, they would be taught to get money from even younger students.' Mr Lau said the serious-crime situation remained stable and it was the increase in petty crimes such as theft and minor deception cases that accounted for the increase in the overall figures. The detection rate in the first half of the year was 41.7 per cent, a slight increase from the 41 per cent in the same period last year, when the figure reached a 10-year low. Mr Lau said different command regions had strategies to improve detection rates. Both shop theft and deception cases rose 19 per cent, while murders rose to 29 from 22 for the same period last year. There was a sharp rise in taxi robberies, which increased 64 per cent to 74 crimes in the first six months this year compared with the same period last year. Mr Lau said the force had set up a taskforce with Shenzhen police to investigate fake banknotes, but he said the amount circulating was small.