Katumbi, the leading rival of President Joseph Kabila, attended a hearing in the court in Lubumbashi, the second city of the Democratic Republic of Congo, over the controversial allegations.
Katumbi, the former governor of the mineral-rich Katanga province who has declared his intention to run for the presidency after breaking with his former ally Kabila in September, has denounced the allegations as "a grotesque lie".
An AFP reporter at the scene said police fired tear gas and beat the crowd back with truncheons, while security agents inside the courthouse were trying to eject dozens of lawyers who arrived to support Katumbi.
One of the lawyers, Hubert Tshiswaka, told AFP they had come to offer free legal assistance to Katumbi "and all the other people arrested over this inquiry".
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The flamboyant Katumbi arrived at court at around midday (1000 GMT) for a third day of hearings, dressed in white and visibly stressed, accompanied by his lawyers and members of his family. He left about 90 minutes later.
But regional police chief general Jean-Bosco Galenga denied the allegations made by Katumbi's legal team and said during a press conference outside the courthouse that six of his own men had been injured.
Before Katumbi's arrival, police jeeps had patrolled the area around the court using megaphones to tell bystanders to "return home".
Katumbi has claimed that the investigation into him announced on May 4, following the arrest of four of his bodyguards including an American, is politically motivated.
Katumbi said last week he would run against Kabila in the election, originally due in November.