FACTBOX: What next in Zimbabwe's elections?

(Reuters) - Below are answers to some key questions on Zimbabwe's elections, in which President Robert Mugabe faced an unprecedented challenge to his 28-year rule.

WHAT DO PROJECTIONS SHOW?

Projections by both the ruling ZANU-PF party and an independent monitoring group show that although opposition leader Morgan Tsvangirai is set to beat Mugabe, he will fall short of the 51 percent needed to win outright.

WHAT DOES THIS MEAN?

If no candidate gets more than 51 percent, a second round is required, three weeks after last Saturday's election. The opposition is expected to unite if there is a runoff.

The most likely scenario is that a breakaway faction of the opposition Movement for Democratic Change (MDC) and third candidate Simba Makoni, a former finance minister, will unite behind Tsvangirai. If Makoni's percentage in the projections is added to Tsvangirai's they would get over 56 percent.

WHY IS THE VOTE COUNT DELAYED?

In past elections, results emerged quickly. But this time they are trickling out and no presidential results have been announced. The electoral commission says it is more complicated now because presidential, parliamentary and local elections were held together for the first time. It says it is still collating and verifying presidential results.

The delays have fuelled suspicions that Mugabe is trying to avoid defeat by rigging the result. Analysts say delays increase the danger of rumors and violence and the opposition has suggested Mugabe is trying to provoke street demonstrations that he can crush, citing the interests of law and order.

WHAT DO THE PARLIAMENTARY RESULTS SHOW?

So far the opposition and government are running almost even with more than half the 210 parliamentary constituencies declared. ZANU-PF has a small lead but that would be wiped out if the two factions of MDC united.

The ruling party projection shows MDC winning a narrow majority in the lower house of parliament but ZANU-PF retaining control of the Senate.

WHO WOULD WIN A RUNOFF?

Some analysts believe the runoff will give ZANU-PF more time to rig results or intimidate opposition supporters, exploiting their control of both the security forces and powerful militia groups.

Security service chiefs have said they would not accept an opposition win. Tsvangirai and some international observers said Mugabe lost the last presidential election in 2002 but he stayed in power.

A run-off could well end with Mugabe being declared victor, leaving political tension and no prospect of saving the economy. Western powers would likely tighten sanctions and Mugabe's power within the party may be weakened. He would be expected to purge suspected Makoni allies.