MINSK: Riot police harshly detained more than 400 demonstrators in Belarus on Sunday as tens of thousands of people took to the streets, on the eve of crunch talks between strongman Alexander Lukashenko and his main ally, Russia's Vladimir Putin.

More than 100,000 people are estimated to have marched in Minsk on each of the past four weekends to demand Lukashenko resign over a disputed August 9 presidential election, which he claimed to have won by a landslide.

AFP journalists said a similar number took part in the latest demonstration, with huge crowds flooding the streets despite an intensifying police crackdown.

Masked police officers in uniform and plain clothes violently detained people who gathered for the "March of Heroes" demonstration, pushing or punching them, video posted on the Belarusian news site Tut.by showed.

Police also resorted to the use of a pump action shotgun, firing a "warning shot" in the air during a scuffle, the interior ministry said.

Access to mobile internet was limited and central metro stations closed, with authorities moving police vans, military vehicles and barbed wire into the centre ahead of the protest.

"More than 400 people were detained in various districts of the capital," the interior ministry said in a statement, adding that those detained were carrying flags and "offensive" placards.

Thousands of demonstrators planning to head towards Lukashenko's Palace of Independence residence and a second at the upscale Drozdy compound were blocked by police, with some officers seen dragging people across the tarmac.

Thousands more protesters took to the streets in other cities including Gomel, Grodno and Brest, where police used water cannon against demonstrators.

Belarusians have been demonstrating against Lukashenko's disputed re-election for a month, with the protest movement showing no sign of dying down.