A Moscow-led military alliance dispatched troops to help quell mounting unrest in Kazakhstan on Thursday as police said dozens were killed trying to storm government buildings.

Long seen as one the most stable of the ex-Soviet republics of Central Asia, energy-rich Kazakhstan is facing its biggest crisis in decades after days of protests over rising fuel prices escalated into widespread unrest.

Under increasing pressure, President Kassym-Jomart Tokayev appealed overnight to the Russia-dominated Collective Security Treaty Organisation (CSTO), which includes five other ex-Soviet states, to combat what he called "terrorist groups" that had "received extensive training abroad".

Within hours the alliance said the first troops had been sent -- including Russian paratroopers and military units from the other CSTO members -- in its first major joint action since its founding in 1999.

"Peacekeeping forces... were sent to the Republic of Kazakhstan for a limited time to stabilise and normalise the situation," the CSTO said in a statement, without specifying the number of troops involved.

The CSTO's current chairman, Armenian Prime Minister Nikol Pashinyan, earlier announced the alliance would agree to the request, saying Kazakhstan was facing "outside interference".

Footage released by the Russian defence ministry showed military transport planes being loaded with troops and armoured trucks before taking off from a snowy runway for Kazakhstan.

In the worst reported violence so far, police said dozens of people were killed in overnight battles with security forces at government buildings in the country's largest city Almaty.

"Extremist forces tried to assault administrative buildings, the Almaty city police department, as well as local police commissariats. Dozens of assailants were eliminated," police spokesman Saltanat Azirbek was quoted as saying by Russian news agencies.

More than 1,000 wounded 

Tokayev said in a televised address early Thursday that "terrorists" were seizing buildings, infrastructure and small arms, and battling security forces.

Military forces had deployed en masse in the streets of Almaty and were firing live rounds, according to footage shown Thursday on Russian television.

Videos on social media showed pillaged shops and burned buildings in Almaty, automatic gunfire in the streets and residents screaming in fear. 

Officials said more than 1,000 people had been wounded in the unrest, with nearly 400 hospitalised and 62 in intensive care.

As of midday Thursday, more than 350 security officers had been wounded and 13 killed, including two who had their heads cut off, officials told local media.

There were reports of looters attacking and ransacking the offices of local television channels and surrounding two hospitals in Almaty.

Protests spread across the nation of 19 million this week in outrage over a New Year increase in prices for liquid petroleum gas (LPG), which is widely used to fuel cars in the west of the country.

Thousands took to the streets in Almaty and in the western province of Mangystau, saying the price rise was unfair given oil and gas exporter Kazakhstan's vast energy reserves.

Protesters were reported to have stormed several government buildings on Wednesday, including the Almaty mayor's office and the presidential residence.

The full picture of the chaos was unclear, with widespread disruptions to communications including mobile phone signals, the blocking of online messengers and hours-long internet shutdowns.

The protests are the biggest threat so far to the regime established by Kazakhstan's founding president Nursultan Nazarbayev, who stepped down in 2019 and hand-picked Tokayev as his successor. 

Tokayev tried to head off further unrest by announcing the resignation of the cabinet early on Wednesday, but protests continued.

State of emergency 

Tokayev also announced he was taking over from Nazarbayev as head of the powerful security council, a surprise move given the ex-president's continued influence.

With protests escalating, the government late on Wednesday said a state of emergency declared in protest-hit areas would be extended nationwide and in effect until January 19.

It imposes an overnight curfew, restricts movements and bans mass gatherings. 

Much of the anger appeared directed at Nazarbayev, who is 81 and had ruled Kazakhstan since 1989 before handing power to Tokayev.

Many protesters shouted "Old Man Out!" in reference to Nazarbayev and images posted on social media showed a statue of the ex-president being torn down.

The EU and the UN called for "restraint" on all sides, while Washington urged authorities to allow protesters to "express themselves peacefully."

Kazakhstan, which tolerates little real opposition, is a key ally of Russia but has also sought good ties with the West and China. 

A major oil and gas exporter and the world's biggest producer of uranium, the country has signed lucrative deals with international energy companies like US firm Chevron, which controls half of the massive Tengiz oil field.

Critics say widespread corruption has meant little of that money reaching ordinary people, with average monthly salaries in the country of less than $600 (530 euros).