Leftist candidates were projected to win the most seats in Colombia's Senate on Sunday, as well as contend for second place in the lower house, in what would be their best ever electoral result. 

With more than 90 percent of polling stations counted, the left's Historical Pact coalition is set to win 17 of the 102 seats in the upper house, partial results from the electoral authority showed. 

In the lower house, it looks set to take 25 of the 165 seats in a tie with the Conservatives and behind the Liberals.