Bolivia's Indian ethnic groups are largely supportive of Mr Morales' plans
Bolivians have backed a new constitution that aims to empower the country's indigenous majority, partial results from a referendum show.
With about 30% of the vote counted, some 53% of the voters supported the changes, electoral officials said.
But at least four of Bolivia's nine regions voted "No".
President Evo Morales claimed victory in the referendum that would also allow Bolivia's first indigenous leader to stand for a second consecutive term.
Addressing supporters outside the presidential palace, he said the result marked the birth of a new Bolivia.
"Brothers and sisters, the colonial state ends here," President Morales, an Aymara Indian, told crowds in front of the presidential palace in La Paz after results emerged.
"Now Bolivia is being re-founded," he said.
"Here we begin to reach true equality for all Bolivians."
Evo Morales is Bolivia's first indigenous president
Support for Mr Morales was highest in the western highlands where indigenous people form the majority.
"A new era is starting now in which indigenous people will be the citizens of this country. I think this is the most important part of this constitution," said Elisa Canqui, who represents one of the Indian communities in La Paz.
Only some 50 years ago Indians of Aymara and Quechua descent were not allowed to walk in the central square of La Paz.
Now the new charter will give sweeping rights to Bolivia's 36 indigenous groups in the areas of government, the judiciary and land holdings.
But the polarisation that has dogged the country since Mr Morales took office in 2006 is unlikely to diminish, says BBC Latin America analyst James Painter.
Many Bolivians of European or mixed-race descent in the fertile eastern lowlands, which hold rich gas deposits and are home to extensive farms, rejected the charter.
Re-election: Allows Mr Morales to stand for re-election in Dec 2009
Indigenous rights: Stresses importance of ethnicity in Bolivia's make-up. A whole chapter devoted to indigenous rights
Autonomy: Power decentralised, four levels of autonomy - departmental, regional, municipal and indigenous
Resources: Sets out state control over key economic sectors, state sovereignty over vast natural gas fields
Judiciary: Indigenous systems of justice same status as official existing system. Judges will be elected, and no longer appointed by Congress.
Land: New limit on ownership 5,000 hectares (12,355). But measure not retroactive.
The referendum was badly defeated in the opposition strongholds of Santa Cruz, Tarija, Beni and Pando, early results suggested.
"The 'No' vote has put the brakes on the fools who wanted to destroy our country," said opposition leader and Santa Cruz Governor Ruben Costas.
The original draft of the constitution was more radical but Mr Morales made concessions after violent protests against his rule, including a promise that he would not try to win a third term in 2014.
Elections are set for December, when the president, vice-president and Congress will be chosen.
Under pressure from wealthy ranchers, who feared their farms would be broken up and handed over to the poor, Mr Morales also revised the charter so that limits on land holdings will only apply to future land sales.
The new constitution enshrines state control over key economic sectors, and grants greater autonomy not only for the nine departments but also for indigenous communities.
But these clauses regarding layers of autonomy could lead to a raft of competing claims, correspondents say.
The exact implementation of the new charter is also far from certain.
Several articles have to be approved in Congress where Mr Morales does not have a majority in the Senate.
Analysts say that another problem facing the Morales administration is that in the last three years it has benefited from the commodity boom but is now facing a major fall in the price of its main exports, minerals and gas.
Final results are expected in about 10 days.