Demonstrators began their march calmly late morning on Thursday and continued into the night, blowing whistles and waving Togo's green, yellow and red flag, with a heavy security presence stationed at major intersections.
The protesters were blocked from heading to the presidency and shouted "Liberate, liberate Togo!", according to AFP journalists on the scene.
A banner unfurled in front of the armed officers called on "soldiers and police to pledge allegiance to the people", as rain began to fall.
"We're not moving from here," said one protester, Edem Agbogbo. "We're waiting for the green light from our leaders to force our way through."
Togo's political opposition has long demanded the introduction of a two-round voting system and a limit to the number of terms a president can serve.
Gnassingbe, who has repeatedly promised to look into the reforms but never implemented them, took power in 2005 after the death of his father, Gnassingbe Eyadema, who was installed as head of state of the tiny West African nation in 1967 after a military coup.
"We are going to stay on the streets until he (Faure Gnassingbe) listens to us," another protester, Jonas Badagbo, told AFP.
"We want Faure to re-establish the 1992 constitution and him to leave office," added the 29-year-old.
A woman who gave her name as Agnes, 64, said: "I've known the same family since I was 14. Let's liberate Togo so these children can see something else.
"We're tired. Enough is enough," she said.
The veteran political opposition leader Jean-Pierre Fabre told AFP he was moved by the thousands of people who had turned out for the protest.
"To see the Togolese people rise up as one is a source of great satisfaction," he said. "I'm overcome with emotion."
Observers say the scale of the protests is unprecedented, which explained the heavy security. One said there was "a lot of tension in the air" and more people than Wednesday.
Internet problems
Mobile internet services were cut in Togo on Thursday, after an estimated 100,000 or more protesters turned out across the country on Wednesday.
On social media sites Facebook and Twitter, which were still accessible using intermittent Wi-Fi access in the capital, users called for services to be restored.
The Internet Without Borders group said the shutdown was "an attack on Togolese citizens' freedom of expression online".
Amnesty International's Togo director, Aime Adi, told AFP by telephone that the internet and mobile phone networks were completely off in several cities in northern Togo.
Information minister Gilbert Bawara has told several local radio stations that the government reserved the right to impose restrictions on access to the internet.
Amnesty's Adi said similar protests were taking place outside Lome, including in Sokode, 300 kilometres (185 miles) north of the capital, where two protesters were killed last month.
In Bafilo, north of Lome, about 100 protesters had blocked traffic on the main road, he added.
Faure Gnassingbe won elections in 2010 and 2015 but the opposition disputed the results and hundreds of people lost their lives during violent protests after the votes.
Transparency International ranked Togo 116th out of 176 countries in its annual corruption Perceptions Index last year.
Togo was 166th out of 188 countries in the UN Development Programme's human development report, which looks at areas such as levels of income, health and education.
AFP contacted the presidency repeatedly for comment on the protests but without response. On Tuesday, a tentative plan was announced for constitutional reform.
But parliament, which has to approve it, is not due to return from its summer break until next month and exact details of the plan were vague.
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