Sri Lanka's parliament will convene Tuesday in its first session since a state of emergency was imposed as the country grapples with protests and mounting demands for the president's resignation over a worsening economic crisis.

Severe shortages of food, fuel and other essentials -- along with record inflation and crippling power cuts -- have inflicted widespread misery across the island nation, which is enduring its most painful downturn since independence from Britain in 1948.

President Gotabaya Rajapaksa's once-powerful SLPP ruling coalition suffered a string of defections ahead of the parliamentary session, undermining his ability to ratify a state of emergency imposed on Friday to quell the growing public protests. 

The state of emergency is due to expire on Thursday next week unless it is ratified in a parliamentary vote.

As parliament reconvenes, the speaker is obliged to officially inform MPs that the state of emergency has been declared, raising the prospect of opposition demands it be put to a vote immediately -- which the government would likely lose.

All opposition parties and even some lawmakers from Rajapaksa's own party have announced their intention to vote against extending the ordinance.

"Our party no longer has a mandate to govern," former minister Nimal Lanza told reporters in the town of Negombo, adding that about 50 lawmakers previously allied with the government would instead sit as independents. 

Every member of Sri Lanka's cabinet except the president and his elder brother, Prime Minister Mahinda Rajapaksa, resigned late on Sunday.

But an overture to opposition parties requesting their participation in a unity government was swiftly rejected the next day.

"We will not be joining this government," Eran Wickramaratne of the main opposition Samagi Jana Balawegaya (SJB) party told AFP. "The Rajapaksa family must step down."

Boisterous demonstrations have spread across the country of 22 million despite emergency laws allowing troops to detain participants and a weekend curfew that lapsed on Monday morning. 

Crowds have attempted to storm the homes of over a dozen government figures including the president's house in Colombo, where protesters torched the vehicles of security forces, who responded by firing rubber bullets and tear gas 

However, Wickramaratne told AFP on Monday that the opposition would not be voting for the emergency orders. "We'll see what happens tomorrow, it is going to be a decisive day."

A critical lack of foreign currency has left Sri Lanka struggling to service its ballooning $51 billion foreign debt, with the pandemic torpedoing vital revenue from tourism and remittances.

The result has seen unprecedented food and fuel shortages along with record inflation and crippling power cuts, with no sign of an end to the economic woes.

Economists say Sri Lanka's crisis has been exacerbated by government mismanagement, years of accumulated borrowing and ill-advised tax cuts.

The government plans to negotiate an IMF bailout, but talks are yet to begin.