Zimbabwean President Robert Mugabe says he is confident his ruling Zanu-PF party will win next month's elections.
Mugabe has ruled Zimbabwe since independence in 1980
He was speaking at a rally to launch his campaign for a sixth term in power and celebrate his 84th birthday.
Thousands gathered at the rally in the town of Beitbridge on the border with South Africa.
Launching his manifesto in the eastern town of Mutare, opposition leader Morgan Tsvangirai, said Zimbabwe was bleeding under "dictatorship".
The presidential, legislative, senate and local council polls are scheduled for 29 March.
Mr Mugabe has been in power since Zimbabwe gained independence from Britain in 1980.
Zimbabwe is suffering an economic crisis, with annual inflation of 100,000%, and unemployment at 80%. There are also severe food and fuel shortages.
Many of Zimbabwe's problems have been blamed by the opposition and Western countries on the policies of President Mugabe.
But he told his supporters that his party would win the elections "resoundingly" and he was ready for a fight with those who criticised his presidency, including President Bush and British Prime Minister, Gordon Brown.
"It is the sanctions that they have imposed which have caused a great deal of harm on the economy," he said.
Mr Tsvangirai - who leads the Movement for Democratic Change (MDC) - is one of three candidates challenging him in the presidential poll.
The opposition MDC wants Mugabe to go after 28 years in power
The others are independent candidates - former Finance Minister Simba Makoni and Langton Towungana.
Mr Makoni, 58, has pledged to turn round the country's economic fortunes if elected.
He has been expelled from Zanu-PF, and Mr Mugabe has compared him to a prostitute.
Launching his campaign before thousands of supporters in Mutare, Mr Tsvangirai said:
"All of Zimbabwe is in the custody of a dictatorship. We're all bleeding, but we're marching on. We're weak and with hunger, but we're stronger with anger."
He said the Zimbabwean economy was "an enclave economy that is uneven, unequal and virtually dead".
"Zimbabwe is one of the world's great humanitarian crises," he said.
BBC southern Africa correspondent Peter Biles says Mr Mugabe's annual birthday celebration is always a lavish occasion, and the state media have poured adulation on the Zimbabwean president this week.
Across the border in South Africa, Zimbabwean exiles have been staging an anti-Mugabe demonstration.
Roy Bennett of the MDC addressed the crowd of about 200 exiled Zimbabwean activists.
"After 28 years, a man who is now 84 years old is having a birthday party. A birthday party while everybody around him is starving and dying."