Typhoon Chanchu, the strongest storm ever to enter the South China Sea in May, moved within 800km of Hong Kong last night, prompting the Observatory to issue the No 1 standby signal at 9.40pm. The Observatory said the typhoon, which killed 37 people in the Philippines, had maximum wind speeds near its centre of up to 170km/h. At 1am, Chanchu was centred about 710km south of Hong Kong and was forecast to move north at about 14km/h towards the coast of Guangdong. The Observatory did not rule out the possibility of issuing the No 3 strong wind signal tonight or early tomorrow morning as winds were expected to become stronger. Chanchu ripped through the central and northwestern Philippines over the weekend, leaving 37 dead and thousands homeless. The government said building contractors and site management staff in Hong Kong should take appropriate safety measures given the approaching typhoon season. 'When the weather turns bad, engineering staff on site should ensure that all scaffolding and hoardings are secured and taut, and all canvas removed,' a Labour Department spokesman said. The Buildings Department yesterday issued a new set of guidelines on the design and construction of bamboo scaffolding. The guidelines call for inspection of scaffolding every 14 days during normal weather and more frequent checks during storms. They also map out the approved standards for bamboo scaffolding. A spokesman for the department said the guidelines were not binding, but warned that contractors could face legal action if sub-standard scaffolding collapsed and caused injuries. Last summer, scaffolding measuring 20 metres by 50 metres collapsed on a bus in San Po Kong during a storm, while signboards and containers fell in other parts of the city causing traffic chaos for hours.