"According to the information that reached the (IEC) contact centre the BDP has already won 30 seats. That implies the BDP has already won the majority," Maroba said.
The main opposition Botswana National Front had only three seats, on a par with its offshoot, the Botswana Congress party.
Langston Motsete, a BDP party election committee member, told the AFP news agency: "We are the new government again."
"According to the information that reached the (IEC) contact centre the BDP has already won 30 seats. That implies the BDP has already won the majority"
Oscar Maroba, spokesperson of the Independent Electoral Commission
This year's elections in Botswana, the world's biggest diamond producer, were the toughest yet with bitter infighting in the BDP and an economy hard hit by falling diamond revenues.
The BDP was tipped to win - with little contest from a weak opposition - after overseeing four decades of stability.
But there is growing unease over Khama's leadership style, said to be authoritarian and non-consultative.
Khama's approach has made him popular abroad, having often broken ranks with regional leaders' unwillingness to criticise democratic abuses by Robert Mugabe, Zimbabwe's president.
Khama, 56, told the AFP this week that Harare's fragile unity government was "limping along" and faced collapse, warning he would not recognise a Mugabe-only government as chaos across the border overshadowed Botswana's peaceful poll.
Botswana is Africa's flagship democracy and is often hailed for its stability on a continent where elections tend to be chaotic.
An observer mission from the Southern African Development Community (SADC) bloc hailed the peaceful conduct of the polls, saying they were calm with no reports of intimidation.
"It was a peaceful way of voting ... everything was really calm," said Henrique Banze, deputy foreign minister of Mozambique and leader of the 88 SADC observers.
Despite a strong growth rate, the global recession has highlighted the need to diversify the economy from diamonds which contribute a third of the nation's gross domestic product.
Khama, the son of Botswana's founding father and chief of its largest tribe who remains hugely popular in rural areas, faces several challenges as his government battles high poverty and unemployment rates.
The diamond industry employs just over 5,000 people and unemployment and inequality are high, with 47 per cent of the population living on less than one dollar a day.
Botswana also has the world's second-highest rate of Aids, with one in four adults estimated to carry the HIV virus.