Prime Minister Sheikh Hasina's ruling party won Bangladesh's election with a thumping majority, the country's Election Commission said early on Monday, giving her a third straight term following a vote that the opposition rejected as rigged.

An alliance dominated by Hasina's Awami League won 287 of the 298 seats for which results have been declared for the country's 300-strong parliament. The main opposition Bangladesh Nationalist Party, which boycotted the last poll in 2014, won just six seats.

"My congratulations to the Awami League," Helal Uddin Ahmed, secretary of the Election Commission Secretariat, said in a televised speech, reading the results.