Juan Karita, Associated Press
Supporters of Bolivia's President Evo Morales march in La Paz on Saturday during a ceremony showcasing a new version of the constitution that's up for vote.

SANTA CRUZ, Bolivia — Tens of thousands of Bolivians celebrated a declaration of greater independence from President Evo Morales' pro-indigenous government on Saturday, massing in this eastern city, the nation's biggest and wealthiest.

Simultaneously, throngs of Morales' backers filled the main plaza in La Paz, the highland capital, to celebrate a new draft constitution that would concentrate more power in the hands of central authorities.

The dueling rallies, though peaceful, reflect rising tensions over the leftist project Morales has charted in South America's poorest nation since his December 2005 election.

Morales' allies approved this month a draft constitution that would help him spread more of Bolivia's wealth to its poor, indigenous majority, which is concentrated in the country's arid west. The new charter goes to voters for approval next year.

Claiming the new constitution will erode their authority and finances, leaders of Bolivia's four eastern states — led by Santa Cruz — moved this week to declare autonomy.

The states, including Pando, Beni and Tarija, represent some 35 percent of Bolivia's population of more than 9.5 million and are pushing for a federalist system in which they would share fewer revenues with the central government.

A Santa Cruz "autonomy statute," which state voters would have to approve in coming months, would create a separate police force and insist on state control of lands.

It clashes with the new draft constitution, which was approved this month by a special national assembly despite a boycott by the country's main opposition party. An article of the constitution that would dismantle of major agricultural estates will be voted on in a separate public referendum.

Bolivia's largest estates are in this agribusiness-heavy region, which is also home to the country's main oil and natural gas exporters.

The standoff between the more prosperous east and traditionally poor highland west could be mediated by European Union diplomats in coming days, presidential spokesman Alex Contreras said.

In La Paz on Saturday, tens of thousands marched as Morales, the country's first indigenous president and a coca growers' union leader, looked on.

Vice President Alvaro Garcia has called the Santa Cruz autonomy statute "illegal and separatist," while its proponents insist it honors the central government's powers over the military and foreign policy, among other things.

Although festivities in Santa Cruz were peaceful, marked by musical performances, a small bomb exploded at midday just outside the city's main courthouse, police said. Windows were broken but no injuries were reported.

In Santa Cruz, T-shirts and hats were sold with the inscription "Santa Cruz, Autonomous!"