Provincial governments have been ordered to immediately inform Beijing of labour tensions after the weekend bus blast in Wuhan. Beijing officials suspect the explosion, which killed 16 and injured 30 people on Saturday, may have been triggered by disgruntled workers. Departments in the capital had telephoned Wuhan authorities in an attempt to find the cause of the explosion, a Labour Ministry official said. Investigations are continuing and disgruntled workers and Xinjiang separatists are seen as key suspects. Beijing officials are concerned the explosion might fuel further unrest. Workers' demonstrations against delayed salary payments and massive lay-offs have increased in the past 10 months. Beijing authorities earlier ordered provincial governments to report signs of instability once every three months, but the order was met with indifference. 'Local governments are reluctant to report cases of unrest since they feel this is a local affair and do not want the central Government to intervene,' the Labour Ministry official said. Tensions would worsen if workers' grievances were not dealt with promptly, he added. A new order was issued after the weekend blast, instructing local senior cadres to treat workers' grievances seriously. 'A central order has been issued requiring all provincial governments to report to Beijing without delay any signs of workers' agitation in an attempt to build up a centralised information network on possible social unrest,' the official said. An internal report last year revealed that two bombs found in Beijing last March were placed by laid-off workers. Sources said the report confirmed that a bomb that exploded on March 7 on a bus in the capital, killing three people and injuring 10, was placed by Xinjiang separatists. But two other bombs found in the capital the same month were placed by sacked workers.