National Super Alliance (Nasa) flag bearer Raila Odinga, his running mate Kalonzo Musyoka and co-principals Moses Wetang'ula and Musalia Mudavadi have arrived at Bomas of Kenya.
Deputy President William Ruto, who is also President Uhuru Kenyatta's running mate has also arrived at Bomas of Kenya.
The Nasa leaders went into a meeting soon after arriving at the venue.
President Kenyatta has not yet arrived at Bomas.
The Independent Electoral and Boundaries Commission (IEBC) had earlier said they have so far received Form34B from 273 constituencies and is waiting for remaining 17 to finish tallying of presidential results.
IEBC Chairperson Wafula Chebukati said forms yet to be received are from Nyali, Mvita, Lagdera, Wajir East, Mandera West, North Imenti, Mwingi North, Ndaragwa, Mathira, Kitui West, Turkana North, Kasipul, North Mugirango and Embakasi West.
Mr Chebukati made the announcement and said the commissioners are going into a meeting with chief agents of presidential candidates.
He said the next update will be at 2.30pm.
Outside Bomas of Kenya, preparations for the announcement of the final presidential results are ongoing.
There has been a dramatic increase in the number of security officers, including senior members of the presidential escort, at the venue.
A lounge, formerly used by VIPs in the past few days, is now clearly marked “Presidential candidates only’.
Some two seats, normally used by the President, have also been brought in.
The Presidential Strategic Communications Unit team has also arrived at Bomas.
A number of elected leaders, diplomats and Cabinet secretaries have also arrived at the venue.
Notably present is Garissa MP-elect Aden Duale, Foreign Affairs Cabinet Secretary Amina Mohamed, who was seen chatting with diplomats.
Other CSs at Bomas are Raychelle Omamo (Defence) and Najib Balala (Tourism).
US Ambassador to Kenya Robert Godec is also at the venue.
Following the development, some companies, including banks, have asked their employees to go home.