A state of emergency was in force in Uzbekistan's autonomous Karakalpakstan region Sunday after eyewitnesses told AFP that police had broken up a second night of anti-government protests in the administrative centre Nukus.

Strongman leader Shavkat Mirziyoyev was visiting the region for a second time in an attempt to calm a crisis that saw thousands take to the streets Friday and caused him to backpedal over draft constitutional amendments that would have weakened the republic's autonomy.

Internet in the region remains restricted but a drip of videos, mostly shared via the Telegram app, has raised concerns that a security crackdown has left multiple people dead.

Uzbek authorities have made no mention of any casualties so far, and lawmaker Bobur Bekmurodov complained of "shameless provocations" as internet users shared footage of men in uniform moving through a street covered in red liquid on Twitter.

"Dear friends, please do not become part of this shameless provocation. Check the information. It is just red color water. Please, share the truth!"

The size of the protest on Friday was unprecedented for the Karakalpakstan region and possibly Uzbekistan, which saw over 170 people killed during unrest in 2005 in the city of Andijan according to an official toll considered conservative at the time. 

Police said Saturday they had detained "organizers of riots" but did not provide figures.  

Two Nukus eyewitnesses speaking on condition of anonymity confirmed to AFP that a smaller group of protesters had gathered close to a city market before police broke up the demonstration using what appeared to be tear gas and smoke grenades. 

Mirziyoyev on Saturday ordered a month-long state of emergency in the region to "ensure the safety of citizens, protect their rights and freedoms (and) restore law and order".

Eyewitnesses said Nukus was quiet on Sunday morning, with police and military patrolling the streets.  

Impoverished Karakalpakstan takes its name from the Karakalpak people. They are well represented in cities such as Nukus, but now constitute a minority overall in the western region of two million people.

Mirziyoyev's press service said Saturday night that he had met with lawmakers of Karakalpakstan's parliament and pledged articles of the constitution concerning the region would remain unchanged "on the basis of... the opinions stated by residents of Karakalpakstan".  

The proposed changes that angered residents included an article removing the autonomous republic's constitutional right to secede from Uzbekistan via referendum.

One amendment set to remain in the draft document will allow presidents to run for seven-year terms, directly benefitting 64-year-old Mirziyoyev, who crushed token opponents to secure a second five-year term in October. 

The draft constitution is expected to be put to a popular referendum in the coming months.