Government supporters carried national flags as they paraded through the streets and lit firecrackers, despite an official week-long ban on public celebrations.
President Mahinda Rajapakse said he saw the overwhelming majority for his United People's Freedom Alliance (UPFA) as a vote for his economic policies and the defeat of Tamil Tiger guerrillas in a major military offensive last year.
"This outstanding victory is an endorsement of the 'Mahinda Chintana' (Mahinda vision)," Rajapakse said in a statement on Friday night.
"I asked you for a strong parliament that can meet any challenge," he said.
"I sincerely thank you for giving me an unprecedented majority that will help make Sri Lanka an example to the rest of the world.
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The UPFA secured 117 seats in the 225-member assembly with another 45 seats still to be declared. The main opposition United National Party (UNP) was reduced to 46 seats.
UNP leader Ranil Wickremesinghe said the election campaign was marred by wide-spread ab