Yves Leterme took office in March after nine months of political deadlock
Belgian Prime Minister Yves Leterme has tendered his government's resignation to the king after failing to carry out political reforms.
Mr Leterme had set a 15 July deadline to push through measures to devolve more power to the regions.
He took office in March - after nine months of political deadlock - as the head of a coalition of Dutch and French-speaking parties.
King Albert II has yet to decide whether to accept the resignation.
The government coalition includes Mr Leterme's Flemish Christian Democrats from the north as well as Socialists from the French-speaking region of Wallonia in the south.
The prime minister was due to present a state reform deal in a speech to parliament on Tuesday.
Before last June's general election, Mr Leterme had promised his supporters even more devolved powers for regional governments in a country that is already Europe's most decentralised state.
In French-speaking Wallonia - where unemployment is higher and the economy sluggish - there are fears this would leave their region worse off.
"It appears that the communities' conflicting visions of how to give a new equilibrium to our state have become incompatible," Mr Leterme said in a statement.
He added that "state reform remains essential".
His French-speaking coalition partners said they hoped the government could be kept together.
Three federal regions: Dutch-speaking Flanders in the north; French-speaking Wallonia in the south (which has a German-speaking minority); Brussels, the capital, officially bilingual
Federal state has national responsibility for justice, defence, federal police, social security, nuclear energy, monetary policy
Regional governments oversee education, employment, agriculture, transport, environment
"I think we still have time to find a solution in the hours and next few days within the framework of what we already have," said Deputy Prime Minister Didier Reynders.
"Otherwise we'll have to look for something else."
"The king now has to be given time to consult a number of people. It's far too early to say what will happen next."
The newspapers reflected the atmosphere under headlines like "Total Chaos".
"No one can predict what is going to happen now," said the centre-left daily De Morgen.
Belgium's Dutch and French-speaking communities seem to exist side-by-side, but with little interaction, says the BBC's Dominic Hughes in Brussels.
No single party bridges the linguistic and geographic gulf between Belgium's two regions.
Traditionally, the prime minister comes from one of the majority Flemish parties.