The Wuhan authorities would not comment on the likely cause of the explosion, and refused to say whether it appeared to be a bomb or an accident. But the official Guangzhou Daily in a front-page story yesterday said: "Police initially suspect the explosion was caused by lawless elements planting explosives on the electric-powered bus." It did not offer any suggestion about who these lawless elements might be. At least 30 people were also injured, when the blast ripped apart the bus as it approached a bridge over the Yangtze river.
China was already tightening security ahead of next month's annual meeting of parliament, the National People's Congress, which starts on 5 March. The police are on guard against protests from both Muslim Uighur separatists and the growing ranks of the urban unemployed. A year ago, Muslim Uighur separatists in the far western Xinjiang province planted three bombs on buses in the provincial capital Urumqi, killing nine people. Those explosions took place on the day of Mr Deng's funeral.
Over the past year there have also been a number of bombs set by disgruntled laid-off state enterprise workers, including three small devices last March in Peking, one of which was placed on a bus.
However, there have also been several explosions caused by Chinese illegally transporting large quantities of explosives by trains and buses for use in mining or industry, and it is possible that the Wuhan blast was such a case.
During last month's Chinese New Year holiday, railway stations around China displayed posters with graphic photographs of people accidentally killed on trains because passengers had taken such explosive materials on board.
Wuhan does not seem an obvious target for the Uighurs, who would be more likely to choose targets in Peking or Xinjiang. The central Chinese city does have a rising number of unemployed, as state factories have shed large numbers of employees. However, if Saturday's blast was a bomb, it could also be a case of an individual Chinese with a grievance.