Kazakh police broke up anti-government protests across the country on Saturday, detaining dozens of protesters and cordoning off the main squares of major cities.

Opponents of President Nursultan Nazarbayev, who has been in power since 1989, had called for rallies in all major cities, extending a series of demonstrations that started last month in response to plans to privatize large tracts of farmland.

The protests, which have become an outlet for expressing general discontent with the government, are the Central Asian nation's biggest for more than a decade and continued on Saturday despite pre-emptive detentions of many activists and warnings from the authorities.

At least 100 protesters gathered at one police checkpoint that blocked access to Almaty's main square. Similar-sized groups tried to enter the square at other points, some sang the national anthem.

Reuters witnesses saw police, some in full riot gear, chase protesters down the street, detaining them one-by-one and putting them into buses.

"Why are you just sitting here?" one protester, a young woman in tears, cried out at a group of onlookers.

Police also briefly detained two Reuters reporters but released them after driving them a short distance in a police van.

In the capital Astana, a Reuters correspondent saw police, who also cordoned off the site of the planned protest, detain a few people including journalists.

Raul Uporov, a reporter based in the city of Uralsk in western Kazakhstan, told Reuters by telephone he had been detained by police at the protest. Local newspaper Uralksaya Nedelya, for which Uporov works, posted photographs of another police cordon at the city's central square.

Azamat Maitanov, a reporter from Atyrau, told Reuters by telephone that police had used a similar tactic there too, while Nasha Gazeta newspaper based in Kostanai in northern Kazakhstan reported several people had been detained in that city.

Although relatively small so far, with the biggest no more than a few thousand strong, the recent protests have become the most visible and geographically broad display of discontent against the president's rule since the early 2000s.

The unrest follows a sharp economic slowdown and the depreciation of the national tenge currency by about 45 percent last year as the price of oil, Kazakhstan's main export plunged.

Kazakh authorities had warned that the planned rallies were "illegal" and that police would react.

"Law enforcement bodies are obliged to prevent any violations and immediately take the necessary legal measures including criminal prosecution," Prosecutor General Zhakip Asanov had said in a statement on Friday.

Earlier this week, police and courts detained dozens of activists in several cities who had planned to take part in Saturday's protests. On Saturday, the Interior Ministry declined to say how many people police had detained across the country.

Police also said on Friday they had found caches of Molotov cocktails, gasoline and iron rods near the protest site in Almaty — the kinds of improvised weapons used in protests in fellow ex-Soviet nation Ukraine which toppled its leadership.