Portugal has slid back into political uncertainty after its third government in as many years fell when the prime minister lost a confidence vote in Parliament.

Prime Minister Luís Montenegro lost a confidence vote triggered by an ethics scandal, with Portugal now facing its third general election in four years.

The government, led by the Social Democrats in an alliance with a smaller party, fell amid a controversy that has revolved around potential conflicts of interest in the business dealings of outgoing Prime Minister Luís Montenegro's family law firm.