The security organ of the 15-nation Southern African Development Community (SADC), known as the Troika, was scheduled to meet from 5:00 pm (1500 GMT) Thursday, a Mozambican foreign ministry official told AFP.
"The objective is to discuss security in the region," said Francisco Siueia.
Leaders from Botswana, the Democratic Republic of Congo, Malawi, Mozambique, South Africa and Zambia are expected to attend.
A spokesman for South African President Jacob Zuma said the meeting would focus on Zimbabwe and Madagascar.
"The chairman of the Troika will brief the summit on the progress thus far in terms of the situation in Zimbabwe" as well as Madagascar, said Vincent Magwenya.
SADC has been working to resolve the ongoing disputes that have threatened to derail Zimbabwe's fragile unity government and an aborted power-sharing deal in Madagascar.
The summit was announced just 24 hours before it was scheduled to start, but many regional leaders were already planning to be in Maputo to attend the swearing-in of Mozambican President Armando Guebuza for a second term.
Guebuza currently heads the Troika, which also includes Swaziland and Zambia.
"They will leave the ceremony, go to lunch, then meet" for the summit, said foreign ministry official Siueia. He added that it was possible the meeting would go late into the night.
A senior Zimbabwe government official told AFP that President Robert Mugabe would attend the meeting. However a spokesman for Mugabe's partner in the unity government, Prime Minister Morgan Tsvangirai, said he did not know about the summit and that the prime minister would not attend.
The summit follows a meeting of SADC foreign ministers last week in Maputo to discuss the Zimbabwe and Madagascar crises.
The regional bloc has been due to review progress in Zimbabwe's unity government after a special summit in November broke a deadlock that threatened to sink the deal.
Tsvangirai had withdrawn from his pact with Mugabe over disputes about key appointments and alleged harassment of his supporters, but was persuaded to rejoin after Troika leaders intervened.
South African mediators have since held talks in Harare among the rival Zimbabwe parties to settle the differences threatening to derail the deal.
