Agency reports said Bios home was surrounded by police, at about 6pm when counting of votes began at polling stations.
They were initially refused entry, reports said.
After an intervention by former Ghanaian president and election observer John Dramani Mahama, police were allowed to enter, they said, refusing to comment on the purpose of the raid.
He was able to persuade them to allow us access to the building, said Mohamed Kamara, head of the police criminal investigation.
We came in with a warrant, he added, saying officers observed material on several laptops before dispersing by 8pm.
SLPP spokesman Lahai Lawrence Leema said it was an act of intimidation aimed at rigging elections.
The APC and SLPP have dominated Sierra Leones politics since independence in 1961, but third parties are hoping to make their mark after mounting charismatic campaigns based on the two parties shortcomings.
President Ernest Bai Koroma, who cannot run again after two consecutive five-year terms, has anointed former foreign minister Samura Kamara as his successor for the ruling All Peoples Congress (APC).
A statement released by civil society groups mentioned scuffles in a rural area that were quickly brought under control.
An AFP journalist also witnessed riot police being deployed on the streets of the capital Freetown, with Chief Superintendent Mohamed Bangura confirming two arrests after scuffles involving rival parties.
The export-dependent economy of the mineral-rich but impoverished country is in a dire state following the 2014-16 Ebola crisis and a commodity price slump that has driven away foreign investors.
A presidential runoff is likely, according to experts, as the threshold to win outright in the first round is 55 percent.
The APC broadly relies on the Temne and Limba people in its northern strongholds, while the SLPP is more popular in the south with the Mende ethnic group.
The National Grand Coalition (NGC), headed by former UN diplomat Kandeh Yumkella, is challenging the two-party system by appealing to young and better-educated urban voters deemed less likely to vote along regional and ethnic lines.
Its communications chief said it had reported some irregularities to the National Election Commission (NEC).
Source: NAN