The warning came from the international committee supporting the transition in Congo (CIAT) on Wednesday.
The CIAT said: “Such misrepresentation sows unease among the people and could threaten public order.”
The European commission issued a similar message, appealing for calm and restraint, late on Wednesday.
Benita Ferrero-Waldner, the European external relations commissioner, said: “I call on all the candidates and their supporters to show a sense of responsibility and maintain the climate of calm and serenity that will be vital in coming days and throughout the process.”
The appeals came as some private television stations owned by election candidates – in particular Joseph Kabila, the president, and his rival Jean-Pierre Bemba, the vice-president, – presented the results from some towns and villages as indications of national trends.
The CIAT statement said: “The publication of provisional election results is the exclusive responsibility of the independent election commission.”
The electoral commission and the country’s press regulator published a joint statement criticising the media for “flagrant violation of the electoral law concerning publication of the results”.
It said that such abuses could “disturb the electoral process and create a climate of tension that is pointless and dangerous”.
William Swing, the head of the UN organisation mission in the DRC, said: “It is in the interests of the people and process to be patient and stay calm.”
He was particularly concerned about declarations of victory or fraud allegations before electoral authorities had completed their work.
Final results are not due until late August.
The country is almost the size of western Europe and has almost no hard roads.
Results from 50,000 local polling stations were still being taken to 62 election commission centres on Wednesday.
It was the first multiparty election in Congo in 46 years.