Malawi's president is planning to contest a court decision overturning his election in May last year.
A spokesman for Peter Mutharika said he would lodge an appeal with the Constitutional Court.
On Monday judges annulled the vote, citing widespread irregularities. They ordered a new election within 150 days.
Malawi's governing Democratic Progressive Party has urged its supporters to remain peaceful.
The opposition leader, Lazarus Chakwera, told thousands of celebrating supporters that the verdict was a victory for democracy.
He came a close second to Mr Mutharika, and went to court alleging fraud.