Police were investigating where an explosive device discovered in Yau Ma Tei last night came from. At 5pm, a cleaner found what he thought was a pipe in a laneway off Battery Street, between Nos95 and 105. Smoke started coming out of it and there was a foul smell, so the cleaner alerted police. At about the same time, police received other calls from people in the area saying they had heard a loud bang coming from the lane. Police officers rushed to the site, cordoned off the area and found the object, which was still burning. The Bomb Disposal Squad was called to detonate the device, which was 12cm long and had 'grenade' written on it. Officers from the bomb squad said the poorly made object contained a weak explosive that posed little danger. They took it away for testing. Officers did not know where the device was made or why it was left in the lane. Police inspected nearby buildings and the surrounding area but found no other similar devices.