Supporters of Zambian opposition candidate Hakainde Hichilema have begun celebrating as early election results show him leading in the tightly-fought, tense presidential race.

Zambia’s standing as one of Africa’s most stable democracies is being tested this week in the vote in which President Edgar Lungu is seeking re-election.

Zambia’s president Monday opened a sprawling new Chinese-funded and built terminal at the main airport in the capital, Lusaka, days before crucial polls, warning that election-related violence could shatter the stability of one of Africa’ most peaceful nations.

Zambia is on “the brink of a human rights crisis,” Amnesty International said Monday, alleging that President Edgar Lungu faces is using repressive tactics to win another term in elections set for Aug. 12.