SANTA CRUZ, Bolivia, May 5 (IPS) - The overwhelming vote in favour of autonomy in Bolivia’s richest province has strengthened the challenge to the reforms being ushered in by the government of Evo Morales.

Exit polls indicate that 85 percent of voters in the eastern province of Santa Cruz backed the autonomy statute in Sunday’s election, which was declared illegal by the national government and the electoral authorities.

But the Morales administration and its supporters also claimed a victory, based on the high abstention rate added to the "no" votes and the spoiled ballots, which totalled 49 percent according to their calculations.

Supporters of the government had called for a boycott of the referendum, to weaken its legitimacy.

Election day was marked by violent clashes between government supporters opposed to the autonomy statute -- mainly indigenous migrants from Bolivia’s impoverished western highlands provinces -- and members of the rightwing Santa Cruz Youth Union.

The day after the referendum, the highly polarised country is caught up in uncertainty as to what will happen next.

Bolivia, South America’s poorest country, is basically divided between the western highlands, home to the impoverished indigenous majority, and the much wealthier eastern provinces, which account for most of the country's natural gas production, industry, agribusiness and gross domestic product. The population of eastern Bolivia tends to be of more European (Spanish) than indigenous descent.