Police fired tear gas and clashed with protesters on Friday as tens of thousands joined the funeral of opposition leader Chokri Belaid whose murder plunged Tunisia into new post-revolt turmoil.

Skirmishes erupted on the margins of the funeral procession which turned into a demonstration in Tunis, a city paralysed by a general strike called in protest at Wednesday's assassination of the leftist leader.

The interior ministry said 132 people were arrested and estimated the size of the funeral crowd at 40,000.

"With our blood and our souls we will sacrifice ourselves for the martyr," shouted mourners, who also chanted slogans denouncing the ruling Ennahda party as "assassins".

Ennahda has vehemently denied involvement in the killing.

Belaid, 48, was shot dead at close range by a lone, hooded gunman as he left home for work on Wednesday.

Belaid's widow Besma held up two fingers in a victory sign as a chant of "The people want a new revolution" rang out.

The murdered politician's eight-year-old daughter fainted amid chaotic and emotional scenes as Friday's procession began its three-and-a-half kilometre (two-mile) journey to the cemetery.

"My son is a man who lived with courage and dignity. He was never afraid, he left as a martyr for our country," said Salah Belaid, his father.

"We lost a great hero," Beji Caid Essebsi, a former premier and now a centre-right opposition leader, told AFP.

The opposition has accused Ennahda, the Islamist party that dominates the ruling coalition, of eliminating the outspoken government critic after months of simmering tensions between liberals and Islamists over the future direction of the once proudly secular Muslim nation.

Police fired tear gas at rioters who tried to set fire to cars opposite the cemetery in southern Tunis, sending up thick plumes of smoke and causing some panic.

Mourners jostled for space with news photographers before the burial.

Hamma Hammami, a leader of the Popular Front alliance of leftist parties to which Belaid belonged, gave a graveside oration, followed by a minute's silence.

"Rest in peace, Chokri, we will continue on your path," he told the huge crowd of mourners thronging El-Jellaz cemetery.

In the city centre, police wielding batons and firing tear gas clashed with youths who chanted anti-government slogans on Habib Bourguiba Avenue.

Armoured vehicles and troops deployed along the landmark boulevard, epicentre of the 2011 revolution that toppled autocratic president Zine El Abidine Ben Ali and sparked a wave of Arab world uprisings.

As a general strike called by the powerful 500,000-strong General Union of Tunisian Workers (UGTT) took hold, troops were deployed in the towns of Zarzis in the south and Sidi Bouzid, birthplace of the 2011 uprising.

Police fired tear gas to disperse a demonstration in the central mining town of Gafsa, the scene of sporadic rioting after Belaid's killing.

The general strike is believed to be the biggest since January 14, 2011 -- the day Ben Ali fled to Saudi Arabia, where he remains in exile.

Prime Minister Hamadi Jebali responded to Belaid's murder by saying he would form a government of technocrats. Any reshuffle would have to be confirmed by the national assembly.

But a faction of his Ennahda party rejected the move, fuelling uncertainty as political infighting delays a deal on a new constitution.

Jebali late on Friday insisted he was committed to the plan.

"I stick by my decision to form a government of technocrats and I would not need the support of the constituent assembly," he was quoted as saying by the TAP news agency.

Abu Iyadh, who heads the radical Islamist group Ansar al-Sharia and is on the run accused of orchestrating a deadly attack on the US embassy last September, urged Islamic groups to unite to prevent Tunisia "from plunging into chaos."

"We stress this to the Ennahda movement... that conceding and prostrating in such a decisive moment in our country's history will be political suicide," the SITE Monitoring Service cited him as saying in comments posted on the Internet.

Four opposition groups including the Popular Front said they were pulling out of the National Constituent Assembly, elected in October 2011 but which has failed to draft a new constitution.

The Tunisian League for Defence of Human Rights said threats and intimidation were continuing under the Ennahda-dominated government, and called for politicians to be protected.