The widow of U.S. Senator John McCain, Cindy McCain, is among international observers who are now observing the presidential elections in Ukraine.

She is representing the International Republican Institute (IRI).

"It's Election Day in Ukraine. It is a great honor to have the chance to observe the Ukraine election with IRI Global at such a critical time in the history of Ukrainian democracy," she tweeted on March 31.

All 1,103 polling stations are open in Kyiv. Yet, the police said, eight of them opened with a delay.

Law and order in the capital is provided by about 6,000 police officers. Each polling station is guarded by at least two police officers

Polling stations in Ukraine on March 31 opened at 08:00 Kyiv time and will work until 20:00, inclusively.

A total of 199 constituencies have been created in Ukraine. The approximate number of polling stations, according to the CEC website, is 29,888. Some 101 polling stations are abroad.

Read alsoKyiv Mayor Klitschko goes to polling station by bike to vote at Ukraine presidential election (Photo, video)

The CEC registered 2,344 observers from foreign and international organizations in the presidential elections. More than 135,000 law enforcement officers are involved in ensuring public order in Ukraine on election day.

Ukrainians are voting for 37 out of the 39 candidates on the ballot, as two of the candidates announced withdrawal after the ballots were printed.

According to the calendar plan for the presidential election, the CEC should establish the results of the voting by April 10.

If none of the candidates receives over 50% of the vote on March 31, a run-off vote will be held on April 21 for the two front runners in the first round.

In the event of the run-off, the CEC should officially announce the election results by May 1, 2019, and the inauguration of the newly elected president should take place by May 31.

The new president should take office no later than 30 days after the announcement of the official election results.