Czech President Milos Zeman has appointed Jiri Rusnok prime minister, after his predecessor resigned over a bribery scandal involving a close aide.
Mr Rusnok now has to form a caretaker cabinet. Once that government has been appointed, he must seek a parliamentary vote of confidence within 30 days.
But correspondents say the main political parties oppose this.
Ex-PM Petr Necas quit last week when prosecutors charged his chief of staff with corruption and abuse of power.
Jana Nagyova is suspected of bribing former MPs with offers of posts in state-owned firms. It is alleged this was in exchange for them giving up their parliamentary seats.
Two former MPs, an ex-minister and current and former heads of military intelligence were also detained. All except one have been remanded in custody.
The arrest of the disgraced senior aide has become a fully-fledged power struggle between the president and his parliament, the BBC's Rob Cameron in the capital, Prague, reports.
The outgoing centre-right coalition had put forward parliamentary speaker Miroslava Nemcova as new prime minister. Meanwhile the leftist opposition had demanded early elections.
But under the Czech constitution, the president is under no obligation to respect parliament's wishes.
Mr Zeman defied both sides and seized the initiative in the political vacuum by appointing his ex-finance minister to form a so-called "government of experts", our correspondent says.
Mr Rusnok, 52, served as finance minister in Mr Zeman's government in 2001-2002 and became an economic advisor to the president after his landslide election victory in January.
He said he aimed "to put together the cabinet in two weeks and hopefully have it appointed by that time too".
Correspondents say it is unlikely Mr Rusnok will win a vote of confidence. Formally, he would be required to resign immediately.
However, the Czech constitution is vague about what happens next. Mr Rusnok could theoretically be left to govern in an acting capacity until regular elections are held in May 2014.