Security forces in Zambia have seized weapons and arrested 11 people, including senior opposition figures, allegedly involved in an insurrection plot, the government has said.

The leading opposition candidate in last Thursday's presidential election, Brian Mundubile, was also found at the scene of the raid in the capital, Lusaka, according to the country's top civil servant Patrick Kangwa.

Mundubile described Friday night's raid as "an attempt on my life," adding that "colleagues were shot" in his presence.

With results from more than half of the constituencies, he is trailing incumbent Hakainde Hichilema. Mundubile had earlier claimed victory and alleged there were voting irregularities.

The authorities deny the claims, and in preliminary statements observers described election day as largely peaceful and orderly.

They did, however raise concerns about late electoral reforms, media freedom and access to the media in the run-up to the poll.

Giving more details about the raid, Kangwa said the individuals arrested were connected to "military plans involving foreign nationals and illegal military training camps". He added that they posed "a serious threat to state security" and held "high-grade military weapons", ammunition and other materials intended for use in an armed insurrection.

He alleged that shots were fired at law enforcement officers leading to an exchange of fire.

Among those arrested were Patrick Mwansa, the husband of Tasila Lungu, the daughter of former Zambian President Edgar Lungu, and other politicians.

The suspects are being held in custody at various police stations in Lusaka.

Mundubile had made a series of allegations about the electoral process, including reports of military involvement at tallying centres and irregularities involving ballot boxes.

He later said he was being interrogated by Zambian army officers over two videos he released and alleged he had been assaulted while in custody, which authorities denied.

He also accused Tanzania of sending individuals to interfere in the election, an allegation the Tanzanian government firmly rejected as false and unfounded.

Zambia's electoral commission briefly suspended the counting and announcement of results on Friday, citing violence against polling staff and theft of marked ballot papers.

It lifted the suspension the same day, saying the security threat had been contained.