Kazakhstan cut internet and mobile phone access on Wednesday as its president promised a tough response to what he said were "massive attacks" on security forces.

Days of protests over a rise in fuel prices erupted into clashes with police and the storming of government buildings on Wednesday, in the biggest challenge to the Central Asian country's authoritarian government in decades.

Accusing protesters of "massive attacks on law enforcement" that left several dead and wounded, President Kassym-Jomart Tokayev said he would not tolerate further lawlessness.

"I am obliged to protect the safety and peace of our citizens, to worry about the integrity of Kazakhstan," he said in a televised address. 

"I intend to act as tough as possible," Tokayev said. "Together we will overcome this black period in the history of Kazakhstan."

Protests spread across the ex-Soviet 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 the country's biggest city Almaty and in the western province of Mangystau, saying the price rise was unfair given oil and gas exporter Kazakhstan's vast energy reserves.

After a night of unrest that saw more than 200 people detained, several thousand protesters stormed the headquarters of the local administration in Almaty on Wednesday afternoon and appeared to have seized control of the building.

Stun grenades, tear gas

Police fired stun grenades and tear gas at the crowd, some armed with batons and shields seized from police, but were unable to prevent them from entering the building, an AFP correspondent at the scene said.

Local media reported that protesters then set their sights on the presidential residence in Almaty. Both it and the mayor's office were reported to be in flames.

There were reports of other government buildings being targeted in Almaty and elsewhere, but the full picture was unclear as communications were disrupted. 

Journalists and witnesses inside Kazakhstan could not be reached through the internet or mobile phones.

"Kazakhstan is now in the midst of a nation-scale internet blackout after a day of mobile internet disruptions and partial restrictions," web monitoring group NetBlocks said.

"The incident is likely to severely limit coverage of escalating anti-government protests."

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 ushered Tokayev into the presidency. 

Clashes erupted overnight in Almaty, with police firing stun grenades and tear gas into a crowd of more than 5,000 people that marched through central streets shouting anti-government slogans and sometimes attacking vehicles.

Tokayev moved quickly to try to head off the unrest, accepting the resignation of the cabinet headed by Prime Minister Askar Mamin. 

He also imposed states of emergency in the capital Nur-Sultan, Almaty, and Mangystau province from January 5 until January 19.

An overnight curfew will be in place in the areas from 11:00 pm to 7:00 am, with restrictions on movement in and out.

'Old man out'

The protesters in Almaty yelled "old man out" -- a reference to Tokayev's still-powerful predecessor Nazarbayev -- and "government resign" before police moved in.

Tokayev was handpicked as a successor by Nazarbayev, a close ally of Russian President Vladimir Putin.

One of five ex-Soviet nations in Central Asia, Kazakhstan is of crucial importance to Russia as an economic partner and home to a large ethnic Russian population.

"We are closely following the events in the brotherly neighbouring country," Russia's foreign ministry said in a statement. 

"We support a peaceful solution to all problems... through dialogue, not through street riots and violation of laws," it said. 

Kazakhstan's government tolerates little real opposition and has been accused of silencing independent voices and media.

Spontaneous, unsanctioned protests are illegal despite a 2020 law that passed easing some restrictions of freedom of assembly.

Smaller rallies had been staged in cities across the republic from Sunday, beginning with the town of Zhanaozen in Mangystau.

- Gas price rise outrage -The initial cause of the unrest was a spike in prices for LPG in hydrocarbon-rich Mangystau.

Reports by independent media suggested that Tokayev's announcement of a new price of 50 tenge (11 US cents) per litre, down from 120 at the beginning of the year, failed to weaken the rallies in Zhanaozen and Mangystau's capital Aktau as demonstrators aired new demands.

In 2011, at least 14 striking oil workers were killed in Zhanaozen as police crushed a protest over pay and working conditions, the deadliest unrest since the republic gained independence in 1991.