Shock as people survey explosion aftermath

China's leaders, already under fire for their handling of a school explosion this month, sent a senior official to the scene. A reward of 50,000 yuan ($6,000) - the equivalent of 10 years' average wages - has also been offered.

The explosions tore through four separate blocks which housed cotton mill and railway workers. One five-storey building was reduced to rubble.

Suspect

State newspapers published a picture of the wanted man, Jin Ruchao, who lived in one of the blocks. He is also wanted for the murder of his girlfriend earlier this month.

Officials gave no motive for the alleged attack and did not explain whether he had the expertise to set off four big explosions almost simultaneously.

Security has been stepped up in the wake of the blasts

Local people are visibly shocked by the destruction and voiced fears that there could be more attacks.

"If they don't catch these people soon, everybody will be worried", one worker told the AFP news agency.

There was also speculation in the city that the explosions were connected to fears of unemployment, although the cotton factories targeted are said to be fairly profitable and have not laid off many staff.

China has seen sporadic bombings by disgruntled employees who have been sacked in recent years as state-owned enterprises were restructured.

Shijiazhuang, which has a population of 1.3 million, is a centre of China's cotton textile industry.

Extortion

Last year, the authorities there executed a man who had set off several bombs in public places, including crowded buses and shopping malls.

State media said he had been trying to extort money.

The latest explosions come less than a fortnight after a blast at a school in southern Jiangxi province killed nearly 40 children.

The government initially blamed the incident on a lone madman with a bomb.

But families of the dead say their children were being forced to make fireworks and the blast was caused by illegally stored explosives.