Portugal's ruling centre-right coalition are leading the opposition Socialists in Sunday's general election, early exit polls said, and may even hold onto their majority in parliament.

Prime Minister Pedro Passos Coelho's "Portugal Ahead" coalition was ahead with between 36.4 to 43 percent of the vote to 29.5 to 35 percent for the Socialist former mayor of Lisbon Antonio Costa, according to three polls commissioned by television stations.