The Morgan Tsvangirai-led MDC's spokesman Nelson Chamisa said ZANU PF was burying its head in the sand instead of declaring a national disaster to pave way for more food aid to come into the country.
"ZANU PF is burying its head in the sand rather than declaring the situation a national disaster and forming an inclusive government," Chamisa said in a statement.
International food agencies - that have only resumed operations in some parts of Zimbabwe after Mugabe's government lifted a ban on the relief groups - say Zimbabweans are fast running out of food with many families now surviving on just one meal a day.
Several families in some of the worst affected districts were surviving on wild roots and fruits because they have nothing else to eat, according to aid groups.
The UN World Food Programme (WFP) about three weeks ago called on international donors to make available US$140 million in emergency food supplies in order to prevent Zimbabwe's food shortages from deteriorating into a disaster.
The WFP expects hunger to worsen around January 2009 when an estimated 5.1 million Zimbabweans or about 45 percent of the country's 12 million population will require food aid to avoid starvation.
However, the government rejects relief agencies' assessment of hunger in Zimbabwe as exaggerated in a bid to tarnish Mugabe and ZANU PF.
State media quoted Agriculture Minister Rugare Gumbo on Thursday as having said that some relief groups were hoarding grain meant for food aid in warehouses so that they could portray a dire situation in Zimbabwe.
But Chamisa said Gumbo's claims only helped to show how the governing party was out of touch with the unfolding humanitarian disaster in the country.
"The statement made by Rugare Gumbo . . . shows that ZANU PF is still in denial that the food situation in the country has reached very critical levels," said Chamisa.
The MDC spokesman said a new government would have to make the provision of food its top priority.
Analysts see a government of national unity proposed under last month's power-sharing agreement as the first step to ending decade-long food shortages and economic crisis in Zimbabwe.
However Mugabe and Tsvangirai cannot agree on who should control the most powerful ministries in the unity government - a deadlock that is now threatening to derail the September 15 power-sharing accord.
The Southern African Development Community (SADC) has said it would soon call an emergency summit to try to end Zimbabwe's power-sharing impasse after the regional bloc's special security organ failed to resolve the matter during a marathon meeting with Mugabe, Tsvangirai and another opposition leader Arthur Mutambara in Harare earlier this week.