Voters in Botswana have rejected the country’s long-serving governing party in a result that marks a political earthquake in the diamond-rich southern African nation.

The Botswana Democratic Party (BDP) - in power since independence in 1966 - has won only four parliamentary seats as of Friday afternoon. It will be replaced by the Umbrella for Democratic Change (UDC).

In a phone call to UDC leader Duma Boko, President Mokgweetsi Masisi conceded and congratulated his opponent.

Despite overseeing a dramatic change in Botswana, recent poor economic growth and high unemployment dented the BDP’s popularity.

The party "had got it wrong big time", Masisi told a press conference.

"I will respectfully step aside and participate in a smooth transition process ahead of inauguration. I am proud of our democratic processes and I respect the will of the people."

He has urged his supporters to remain calm and rally behind the new government.

Speaking to Boko on the phone, the outgoing president said: "You can count on me to always be there to provide whatever guidance you might want."

In his first comments to the media since the outcome was clear, Boko, a 54-year-old former human rights lawyer, said: "What has happened today takes our democracy to a higher level. It now means we've seen a successful, peaceful, orderly democratic transition."

"It's a shock to me in terms of the numbers. I'm humbled and I can only pledge to [the people of Botswana] that we'll do the very best," he added.

UDC and other opposition party supporters have been celebrating in the capital, Gaborone, and elsewhere in the country.

"I did not ever think I would witness this change in my life," 23-year-old student Mpho Mogorosi, who had gone on to the streets of Gaborone, told the Reuters news agency.

"The BDP had stayed too long in power and I am proud to be part of the people that removed them for a better Botswana," she said.

The UDC has won 31 seats, according to the latest tally, which means that it has an outright majority in parliament.

It has pledged to adopt a new economic strategy that creates well-paying jobs and distributes wealth that empowers all citizens.

Kgoberego Nkawana, just elected as an MP, told the BBC's Newsday programme that many young people in Botswana remained jobless despite huge deposits of diamonds and a fairly thriving tourism industry in the country.

"The unemployment rate is very very high and people are living literally on handouts from government because there are no jobs. So it's really bad," Nkawana said.

The party has committed to creating 450,000 to 500,000 jobs within five years.

The Botswana Patriotic Front (BPF), supported by former President Ian Khama who split from the BDP, has so far secured five seats while the Botswana Congress Party (BCP) has got 13 seats as things stand.

Political analyst Lesole Machacha said the way that the change in government has been accepted was very impressive.

"It's very rare [on the continent] for a smooth transition to occur," he told the BBC. "This has been very peaceful."

Masisi - in office since 2018 - led the BDP’s failed campaign.

The president ran on a message that his party could bring about "change", but not enough voters were convinced the BDP could do what was needed for the country.

Official results are expected to be announced by the electoral commission later Friday.

Additional reporting from Innocent Selatlhwa in Gaborone.