Zambian President Levy Mwanawasa has likened the current crisis in Zimbabwe to the sinking of the Titanic.
African leaders have been loth to criticise Mr Mugabe publicly
He said the country's economic difficulties were forcing its citizens to leave like passengers jumping from the sinking ship to save their lives.
He called for a new approach as quiet diplomacy was not producing results.
Meanwhile, the UK's leader Tony Blair told the British parliament that the solution to Zimbabwe's problems had to come ultimately from within Africa.
An estimated 3m Zimbabweans, about a quarter of the total population, have fled the country in recent years.
Scores of activists have been arrested and allegedly assaulted after police broke up a banned rally in Harare on 11 March.
Four senior MDC officials were prevented from leaving the country, some to seek treatment for injuries they say were sustained in police custody.
The BBC's Grant Ferrett in Johannesburg says the remarks by Mr Mwanawasa are among the strongest made by any of Zimbabwe's neighbours during years of economic turmoil and political confrontation.
Mr Mwanawasa did not mention Zimbabwe by name, but said a member of the Southern African Development Community (Sadc) had sunk into "serious difficulties".
"As I am speaking right now, one Sadc country has sunk into such economic difficulties that it may be likened to a sinking Titanic whose passengers are jumping out in a bid to save their lives," Mr Mwanawasa said during a state visit to Namibia.
"Zambia has so far been an advocate of quiet diplomacy and continues to believe in it, but the twist of events in the troubled country necessitates the adoption of a new approach."
Our correspondent says such a change would need the support of South Africa.
Over the past week, South Africa has become more forthright in its remarks, but is not yet willing to openly criticise President Robert Mugabe's government.
Mr Blair said the solution to Zimbabwe will not come through pressure applied by the UK.
"That pressure has got to be applied within Africa and particularly within the African Union," the British prime minister said.
"We will continue to do all we can to make sure Africa realises this is a responsibility of Africa as well as the Zimbabwean government."
In Zimbabwe itself, the governor of the central bank, Gideon Gono, has complained that increases of about 200% in the price of petrol had made life unbearable.
He said that the spirit of profiteering had become as deadly as HIV and Aids.
Mr Gono warned that the law would be used to prevent people being ripped off.
Our reporter says the fuel price rises merely reflect the continuing collapse in value of the Zimbabwe dollar.
Mr Mugabe has ruled Zimbabwe for 27 years, but there is increasing discontent over the country's economic crisis.
More than 80% of Zimbabweans are living in poverty, with chronic unemployment and inflation running at more than 1,700% - the highest in the world.