With only five months to go until planned legislative elections in May, in was not immediately clear whether King Philippe would accept Michel's sudden departure.

The palace said a decision is pending but a senior source told AFP the "most likely" outcome would be the crown asking Michel's government to handle the day-to-day business of government until the scheduled vote.

Having lost the backing of the Flemish nationalist N-VA on December 9, Michel had attempted to lead a minority government.

But on Tuesday, during a parliamentary debate, the liberal premier admitted defeat rather than face and probably lose a no confidence vote called by the left-wing and green opposition parties.

Michel, who took office in 2014, lost the backing of the New Flemish Alliance (N-VA) over his support for the UN migration pact, a cause celebre for European anti-immigration parties.

The resignation comes two days after demonstrations against the pact in central Brussels descended into scuffles, with police forced to use tear gas and water cannon to restore order.

After a debate in parliament where opposition parties refused to agree to vote on planned reforms on a case-by-case basis until the May 26 election, Michel announced he would quit.

"I have taken the decision to submit my resignation and it is my intention to go to see the king immediately," Michel said, jumping before lawmakers could push him with a motion of no confidence.

Afterwards, King Philippe received Michel but will hold further consultations before deciding whether to accept his resignation, the palace said in a statement.

Agriculture Minister Denis Ducarne of Michel's liberal MR party, criticised the left wing and green parties for risking "paralysis and crisis for our country" instead of cooperating.

Their support was needed because the N-VA, led by powerful Antwerp mayor Bart De Wever, had made political demands which Michel judged "unacceptable" -- notably on constitutional changes.

The liberal premier has steadfastly defended the Marrakesh migration pact, saying it presented an "opportunity for better European and international cooperation."

The non-binding UN accord, which would promote a common global approach to migrant flows, was initially supported by all four parties in Belgium's coalition.

But the N-VA changed its mind in late October and pulled out of the coalition the day before Michel flew to Morocco to sign the deal, which has come under attack from populist leaders across Europe.

Day-to-day business

Belgium has a history of division between wealthier Dutch-speaking Flanders in the north and the run-down French-speaking former industrial heartland of Wallonia in the south.

Belgium holds the modern record for going the longest time without a government, 541 days in 2010 and 2011, but the country continued to function and even took part in NATO's Libyan intervention.

Michel had been holding together a delicate four-way coalition involving liberals, Flemish Christian Democrats and the N-VA, which wants a separate homeland in Flanders, and he could stumble on.

"Day-to-day business doesn't stop the government from functioning, it just has to do it in a more cautious way," Ecolo party lawmaker Georges Gilkinet told the broadcaster RTBF.

Michel will turn 43 on Friday, and when he arrived in office he was the kingdom's youngest head of government since 1840.

(AFP)