Faure Gnassingbe, candidate of Togo's ruling RPT party and son of the former leader, has provisionally won Sunday's presidential election, officials say.
Faure Gnassingbe has already briefly led Togo
Opposition supporters immediately poured onto the streets of the capital, Lome, erecting burning barricades. They say the poll was rigged.
Many residents stayed indoors as thick black smoke wafted across the city.
The army tried to install Mr Faure after his father died but pressure led him to step down and call an election.
Security forces used tear gas to disperse the opposition protesters in central Lome but shops were reportedly looted in other areas.
In other developments:
- The main opposition party has called on Togolese people to "resist" the government;
- Mr Faure denied vote-rigging and called on the opposition to join a government of national unity;
- In areas of the capital which support the ruling party, activists took to the streets to celebrate, while others patrolled with sticks and bows and arrows to guard against opposition attack;
- A spokeswoman for the Ecowas regional body, which sent observers to the poll, said the "anomalies... were not enough to cast doubt on the good conduct and the credibility of the election";
- Some Lebanese families have fled their homes near the border with Ghana, saying they have been attacked and robbed.
Mr Faure received 60% of the votes, while main opposition candidate Emmanuel Bob-Akitani got 38% of votes cast, said electoral commission chairwoman Kissem Tchangai Walla.
"In view of these results... the candidate of the RPT has been provisionally elected," she said.
However, she said the results did not include areas where ballot boxes had been destroyed.
Faure Gnassingbe: 1.4m votes (60%)
Emmanuel Bob-Akitani: 841,000 (38%)
Source: Electoral Commission (Provisional results)
These issues would be decided by the constitutional court which would announce the final results, she said.
But the BBC's Elizabeth Blunt in Lome says Mr Faure has been declared the winner by such a substantial margin that the result is not likely to be changed.
Mr Akitani's Union of Forces for Change (UFC) has rejected the results.
"We call on the people to resist," said UFC secretary-general Jean-Pierre Fabre.
Civil war fears
Mr Faure, however, urged veteran UFC leader Gilchrist Olympio to join the government.
"He is in the sunset of his political career and we can benefit from his experience," he told the BBC's Focus on Africa programme.
Earlier, UFC leader Gilchrist Olympio, who was barred from standing, said his party would not serve as a minority partner in any unity government.
Mr Olympio was ineligible to stand in the poll because he lives in exile following a 1992 assassination attempt.
This man says he was beaten by security forces
Regional powerhouse Nigeria had said that Mr Olympio and Mr Faure had agreed to share power in a bid to calm tensions.
During the campaign, Mr Faure, 39 was portrayed as the candidate for a new Togo even though his father had run the country for 38 years - in contrast to Mr Akitani, 75.
His support base is in the north, while the opposition is strongest in the south, including Lome.
Last week, the interior minister called for the polls to be postponed for fear that civil war might break out.
He was sacked and sought sanctuary in the German embassy.
Seven people were reportedly killed in pre-election violence.
Mr Faure's father, Gnassingbe Eyadema died in February after ruling Togo for 38 years.
He had seized power in a coup from Mr Olympio's father, Sylvanus, in 1963.