Two home-made explosive devices were hurled at the home of a Yuen Long businessman yesterday in what police believe is part of a campaign of intimidation by debt collectors. One of the devices landed outside the main entrance of the two-storey house in Ma Tin Tsuen in Tai Shu Ha Road East and exploded at about 3.30am. It left a scorch mark on the road. The other device - described by investigators as being as big as a grenade - was hurled into the front yard, but failed to detonate. A dozen residents were evacuated from five houses when police bomb-disposal officers examined the second device at noon. It was removed for examination. 'The device was made of a firework shell and wrapped with adhesive tape. Its fuse had been made longer and had incense attached. The incense had been lit but burned out,' a police officer said. He said it was not very powerful. 'We believe it was a warning rather than an attempt to harm anyone,' he said. Yesterday's incident was the latest attack on the family, which runs a chain of furniture shops. Debt collectors had previously visited the house, where the man lives with his 25-year-old son and a maid. It was attacked with stones and eggs recently. One of his shops in Yuen Long was attacked earlier this month when paint was daubed on the main entrance and the door locks jammed with glue.