Zimbabwe's top electoral official has told a state newspaper that it is likely the country's presidential run-off poll will be delayed.

Zimbabwe Electoral Commission chairman George Chiweshe has told the Sunday Mail that it is very likely the cut-off period for elections will be extended.

He said he thought it was ambitious that the legislature would think that 21 days would be enough.

However, he said, 'they were also wise in that they made provisions for an extension.'

Opposition leader Morgan Tsvangirai warned that failure to hold the second round of voting within the time limit set out in Zimbabwean law risked rendering the election process illegitimate.

The second round should take place within 21 days of the first-round results being announced, making May 23 the last possible day for the ballot, Mr Tsvangirai said.