Two Malawian opposition leaders have been sentenced to 20 months in prison for sedition and inciting violence ahead of the May elections, a court official said on Tuesday.

The convictions in Zomba, 70 kilometres north of the commercial capital Blantyre, mark the first time that Malawi's courts have handed down a sedition conviction since 1993.

Hophmally Makande of the United Democratic Front, led by ex-president Bakili Muluzi, told a rally in March that the party would take "the law into its own hands" if the former leader was barred was running in the elections.

Kamlepo Kalua, who leads the small Malawi Democratic Party, was sentenced for saying at the same rally that: "We can't fear police, we can't fear Bingu," referring to President Bingu wa Mutharika.

The speeches were broadcast on Joy radio, owned by Muluzi.

Magistrate Nyakwawa Usiwa Usiwa said in his judgement that the statements were "emotive and could have incited people to be violent and get angry with the president and cause physical harm to others."

Usiwa Usiwa said Makande's words "were meant to plunge the country into lawlessness."

"I therefore convict and sentence each one of you to 20 months imprisonment with hard labour," the magistrate said.

Defence lawyer Bob Chimkango said he will appeal the sentence.

The two are the first high-profile politicians to be jailed by the administration of Mutharika since he came to power in 2004.

Mutharika won the presidential elections in May, from which Muluzi was barred, and his party clinched a majority in parliament.

He ends second five-year term in 2014.