Touring a voting center in the capital Nairobi, the head of the EU's election observation mission, claimed over 160 observers had been sent out across Kenya.
"We are more than 160 observers basically working in pairs spending roughly 30 minutes in polling stations observing identification of voters, secrecy of voting and all the procedures and we also follow counting of votes and also transmission of results," Ivan Stefanec said.
The election is considered close, and East Africa's economic hub could see a presidential runoff for the first time.
Polls opened Tuesday in the unusual presidential election, where a longtime opposition leader who is backed by the outgoing president faces the deputy president who styles himself as the outsider.
Hundreds of voters lined up hours ahead of polls opening in some locations.
The top candidates are Raila Odinga, who has vied for the presidency for a quarter-century, and deputy president William Ruto, who has stressed his journey from a humble childhood to appeal to millions of struggling Kenyans long accustomed to political dynasties.
More than 22 million people are registered to vote in this election in which economic issues could be of greater importance than the ethnic tensions that have marked past votes with sometimes deadly results.