Rio de Janeiro, May 10 : Brazil's October presidential elections may feature a second round, as support for incumbent President Dilma Rousseff falters and her contenders gain strength, according to an opinion poll.

The latest Datafolha poll, the results of which were declared Friday, showed that support for Rousseff has slid to 37 percent from 38 percent in the previous poll, while Aecio Neves, candidate of the main opposition Brazilian Social Democracy Party, gained four percentage points to 20 percent.

Support for Brazilian Socialist Party candidate Eduardo Campos gained one point to 11 percent, Xinhua reported.

A total of 12 percent of electors said they would vote null and 7 percent remained undecided, the poll showed.

The poll surveyed 2,844 eligible voters from 174 towns over Brazil Wednesday and Thursday, with a two-point margin of error.(IANS)