Ukraine's president and prime minister are set to publish a draft coalition agreement, after an apparent sweeping victory for pro-Western parties in Sunday's parliamentary elections.

With half the vote counted, President Petro Poroshenko and the party of Arseniy Yatseniuk were neck-and-neck with more than 21 per-cent of the vote each.

Both men said they expected other parties to join their coalition talks.

There was no voting in eastern areas controlled by pro-Russian separatists who plan to hold their own elections next Sunday.

As a result, a number of parliamentary seats in the Donetsk and Luhansk regions will remain vacant, as will those for Crimea, which was annexed by Russia in March.