The Zimbabwe prime minister's party says state election officials are dramatically inflating the numbers of voters on lists months ahead of crucial polls.

The party said Tuesday the lists in some voting districts swelled by more than 10,000 names in a 48-hour period, or the addition of about 150 voters a second.

"This is just impossible," said party official Douglas Mwonzora. He said a copy of one Harare district list was obtained on a Monday earlier this month. Two days later, a revised copy showed there were 11,890 more voters listed.

In other districts the names of active party members were missing or misspelled, making them ineligible to vote.

The official voters' registry's has denied tampering with the lists and insists it is just collating data in batches.