By the BBC's Barnaby Phillips

Thousands of delegates from Zimbabwe's ruling Zanu-PF party are gathering in the resort town of Victoria Falls for their annual conference, which starts on Thursday.

President Robert Mugabe is expected to use the event to launch his campaign for the presidential election in March.

With political tension mounting, Zimbabwe's neighbours are concerned that the situation there should not slip out of control.

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Zimbabwe's big neighbour, South Africa, has most to lose should the crisis deepen in the coming weeks.

Already hundreds of jobless Zimbabweans are trying to cross into South Africa every day, and the dramatic fall in South Africa's currency is partially due to a loss of confidence because of the Zimbabwean upheavals.

Other, smaller neighbours, have similar concerns.

Both Malawi and Mozambique fear that thousands of migrant workers could return home from Zimbabwe if they lose their jobs.

In public, African leaders are reluctant to criticise.

The governments of Angola and the Democratic Republic of the Congo - military allies in the Congolese war - will not break ranks with President Mugabe.

It is President Thabo Mbeki of South Africa who has voiced concerns about the possibility of an unfair and illegitimate election.

President Mbeki is trying to build a new relationship between responsible African governments and leading Western powers.

The political violence in Zimbabwe sits awkwardly with his rhetoric of an African renaissance.