URUMQI: It started with some boys fighting over fireworks. It wound up as a clash

between hundreds of villagers from two competing ethnic groups.

Such incidents illustrate the ethnic tension that pervades much of China — and exploded this week in the western region of Xinjiang, taking 156 lives.

The situation is worst in the west, the vast borderlands where Chinese imperial dynasties spilled into traditional homelands of Buddhist Tibetans, Muslim Uighurs, nomadic Mongols and Hui, a Muslim group.

But other areas are not immune: The fight over fireworks broke out in February in Henan province in central China, a day’s drive from Beijing.

In the recent western unrest, anger at the authorities’ handling of a brawl between Uighur and Han factory workers in south China triggered a protest on Sunday 3,000 km away in Xinjiang, the Uighur homeland.

Uighurs beat Han — members of the majority ethnicity in China — and torched their shops and cars.

After security forces quelled the riots, vigilantes on both sides attacked people in the regional capital Urumqi.