Tenants plagued by thefts and break-ins at their ageing public estate flats have been told better security will take five years to implement. The $500 million plan was given a belated go-ahead yesterday, four years after a wide-ranging upgrade was endorsed. About 300 newer blocks and those earmarked for sale have been provided with corridor surveillance cameras, computer locks and entry-phones. But the other 642 blocks, some of which are more than 40 years old, are protected only by a so-called 'basic security system' where lifts and ground floor lobbies have surveillance cameras. The Housing Authority's rental housing committee chairman Chan Kam-man said yesterday the designs of older blocks were partly to blame for the delay. 'In some designs there are many corridors or entrances which allow people many alternatives to go from one block to another,' he said. Most reported crimes in public estates are thefts and burglaries. Tenants say that drug addicts often use vacant flats. Before the security upgrade, tenants will be asked to report the highest risk spots in their blocks, and priority will be given to estates with more crime. Housing Department business director Vincent Tong Wing-shing said the three-phase project would begin a year from now and be completed in four years. Chairman of the People's Council on Public Housing Policy, Fanny Leung Yuk-fung, said that caretakers should patrol the blocks more frequently.