Dozens of Lebanon's main opposition groups and parties on Sunday announced a common position and plan to tackle the country's multiple crises.

The myriad groups active in the unprecedented protest movement that erupted in October last year had subsequently been chronically unable to project unity.

Representatives of the various organisations made their announcement on Martyr's Square, the Beirut hub of the protests that many Lebanese call "the October 17 revolution".

The protests, that briefly rattled Lebanon's hereditary ruling elite, called for an end to sectarianism and corruption through a complete overhaul of the system.

A deadly blast at Beirut port on August 4, one of the largest explosions in history, plunged Lebanon deeper into crisis and revived calls at home and abroad for radical revamp of the state.

"What we are going through here today was caused by the greed of this political system," said a joint document that was read on the podium.

The opposition groups listed the main items of their programme, including sweeping reforms towards a non-sectarian political system and a more sustainable economic model.

"This is an extremely important moment because it shows that 30 odd groups spoke in a single voice, which proves wrong government allegations that there is no opposition," said Naji Abou Khalil, a leader of the National Bloc party.

"This is a first step towards the creation of a structured front that will be able to rise to the challenge of the crisis Lebanon is going through and of the Lebanese people's expectations," he said.

Opposition groups have been meeting intensively since the August 4 blast to draw up a list of figures who could form a competent and independent transition government.

"We have names, we are ready," said Hassan Sinno, a member of the Massirat Watan opposition movement.

"The goal today is make it clear for the political class that there are existing people here, who are in Lebanon and ready to step up," he told AFP.

"Tonight is a very important step," Sinno said.

"It's the first time that groups that are mostly born out of the October 17 revolution have reached an agreement on a common programme," he said.

The umbrella of opposition groups rejected the name that emerged Sunday to replace Prime Minister Hassan Diab, whose government resigned in the aftermath of the August 4 blast.

Mustapha Adib, a little-known diplomat, looked set to be nominated in parliamentary consultations due to take place on Monday after the country's political heavyweights reached an agreement.