Madagascar's constitutional court on Friday ordered the president to form a government of national union in a bid to end a prolonged political crisis.

It issued a judgement requiring President Hery Rajaonarimampianina to dissolve the present government "and proceed to the nomination of a consensus prime minister within seven days."

Madagascar has been rocked by violent protests over electoral laws that the opposition says are designed to bar their candidates from participating in elections expected this year.

The court said the composition of the unity government should proportionately reflect the outcome of the last legislative elections.

The new government will also be tasked with organising "early elections during the 2018 dry season," a period that typically runs from May to September, it said.

Since April 21, hundreds of opposition supporters have occupied a key square in the heart of the capital Antananarivo, demanding Rajaonarimampianina resign.

The row centres on new electoral legislation that the opposition says is loaded in Rajaonarimampianina's favour.

The opposition also accuses the government of trying to sideline opposition candidates out of general elections due this year.

It filed a lawsuit to the constitutional court to demand the president's ouster.

The court, in its judgement on Friday, did not give an opinion on the lawsuit. However, it ordered the high court of justice, which is mandated to rule in disputes involving current and former presidents, to meet "as soon as possible."

The crisis has triggered international concern, with the African Union, the UN and regional bloc Southern African Development Community (SADC) all dispatching envoys to try to defuse the crisis.

Madagascar has seen a series of popular protest movements since the island nation gained independence from France in 1960, often resulting in bloodshed.

In 1972, students lead a revolt against the government. A crackdown after the city hall in Antananarivo was set alight left around 40 demonstrators dead, but the protesters forced the resignation of President Philibert Tsiranana who handed over power to General Gabriel Ramanantsoa.

The first mass demonstration in the capital in 1991 demanded an end of the socialist constitution of 1975, when President Didier Ratsiraka came to power.

General strikes crippled the country and hundreds of thousands gathered peacefully to demand the resignation of the government. However, around 100 people were killed when presidential troops opened fire on marchers near the head of state's palace.

In 1993, Albert Zafy won a presidential election, although three years later Ratsiraka wrestled back power after Zafy was dismissed by the Constitutional High Court.

Antananarivo's mayor Marc Ravalomanana in February 2001 proclaimed himself president, but in the ensuing crisis the capital was blockaded and dozens of people lost their lives on both sides.

Threatened with arrest, Ratsiraka went into exile in France, leaving Ravalomanana in charge.

In early 2009, hundreds of people died as violence spilled on to the streets as supporters of Andry Rajoelina, then the mayor of Antananarivo, demonstrated. In March that year, Rajoelina was named president.

© Agence France-Presse