Kazakhstan's Prime Minister Daniyal Akhmetov has resigned, government officials and web sites said.
No reason was given for the resignation, which will force the whole Cabinet to step down.
The prime minister's office is much less powerful than the presidency, which Nursultan Nazarbayev has held since 1990.
Mr Nazarbayev has developed the country into an increasingly important supplier of oil and gas to the West.
But he has also been criticised for concentrating power in the hands of his family and for failing to deliver elections deemed free and fair.
Mr Nazarbayev is expected to nominate a new prime minister on Wednesday. His nomination needs approval from both houses of parliament, which is also expected.
According to the BBC's Central Asia correspondent, Natalia Antelava, Mr Akhmetov's resignation has been the subject of speculation among political circles ever since several months ago President Nazarbayev openly criticised him for poor planning and overspending.
But in common with most political developments in Kazakhstan, public debate played no part in his resignation and is not likely to be part of the aftermath.
The president's absolute control over the government also means that whoever replaces Mr Akhmetov will not deviate from Mr Nazarbayev's investor-friendly free market economic policies, our correspondent says.
Mr Akhmetov has been prime minister since 2003.