Malaysia's ruling coalition lost its fourth electoral contest on Saturday since coming to power last May, uncovering deepening cracks in the young alliance mired by uncertainty over a succession plan for its top leadership.

The opposition secured a majority of over 15,000 votes to wrest the Tanjung Piai parliamentary seat, a rural constituency in the southern state of Johor, from Prime Minister Mahathir Mohamad's ruling Pakatan Harapan (PH) pact.

The coalition, led by the centrist People's Justice Party, had already been grappling with plummeting public approval over its management of the country in the past year and a half.

Its popularity plunged to 41% in July, well below the 64% rate recorded when it took over power just over a year earlier, according to a survey by independent pollster Merdeka Center.

Discontent within the ruling coalition over Mahathir's reticence on when he will hand over power to rival-turned-ally Anwar Ibrahim surfaced even before the results were officially announced.