Polling stations are open from 9am to 8pm local time (8am to 7pm CET). A preliminary result should be known overnight.
Neither candidate is expected to immediately receive more than half of the votes cast. If this happens, a second round between the two strongest candidates will take place on February 11th.
Niinistö, who led the EU's northernmost country into NATO last year, was not allowed to run again after two six-year terms. His successor is expected to take office on March 1st.