The force was jeered and threatened in several poor neighbourhoods of a city hostile to Joseph Kabila, the president, who leads Jean-Pierre Bemba, the former rebel leader, with results still trickling in.
Youths in Matete hurled abuse and threats at a convoy of more than 20 police vehicles.
Some shouted: "If you want war, we are ready for it!"
Others chanted "thieves, thieves!" and "lets burn them!" as police carrying guns and rocket-launchers made their way through streets clogged with packed minibuses and unemployed people.
Officials said the move was meant to reassure people two days ahead of election results.
A senior police officer said: "We are showing our capacity and our force. This shows we are ready to react, whatever happens.
"Our message is that we are ready to support and protect the population."
Henri Mova Sakanyi, a government spokesman, said that Friday's patrol was a "routine operation".
He said: "This is not intimidation. The police has organised this to improve coordination between the units."
Analysts say that a runoff between Kabila and Bemba in October is likely, as it seems unlikely that Kabila will get the 50 percent needed for a first round victory.
Kabila is Swahili-speaking and from the east of the country while Bemba is from the western Lingala-speaking province of Equateur. Bemba seems to have received most of the votes in the mainly Lingala-speaking capital, Kinshasa.
Monitoring the peace
The election was the country's first free poll in more than 40 years and it was hoped that it would draw a line under a decade of war and chaos.
Voting was overseen by the world's biggest peacekeeping force, but underscored a rift between Congo's east and west and many fear a backlash in the capital if Kabila wins.
Protestors attacked police at anti
election rally in Kinshasa in June
However, three weeks after voting, results being published in Kinshasa not only increase the chances of a second round but also allow Congolese to check how transparent the election was.
Jean Mukalaye, an election official checking that the results he wrote down on election day were the same as those published on Thursday, said: "This shows the transparency of the process.
"It's taken a lot of time and people have been fearing manipulation, but now they are up, this should calm things down.
"We worked hard but it is worth it. The Congo has grown up."