Protests against a new prime minister are spreading in Armenia, with their chief organiser declaring them a "revolution".

Demonstrators object to the country's parliament voting in ex-president Serzh Sargsyan as the new premier.

Opposition MP Nikol Pashinyan made the remarks in the capital Yerevan, a short distance from the country's parliament.

"We must paralyse the entire state system and the power should pass to the people," he said.

"Serzh Sargsyan must see that he has no Armenia to rule in and no people to rule over."

Mr Pashinyan urged protesters in Yerevan and in other cities to blockade state institutions.

Demonstrators in the capital have cordoned off the interior ministry and the prosecutor's office, though police are surrounding the parliament where legislators are confirming Mr Sargsyan.

People are also reportedly massing in the cities of Gyumri and Vanadzor.

Serzh Sargsyan was elected president of Armenia in 2008 and again in 2013, serving two five-year terms before stepping down.

However, following a 2015 constitutional referendum the country shifted from a presidential system to a parliamentary republic - relegating the presidency to a more ceremonial role.

The ex-president had formally stated he would "not aspire" for the prime minister position. But on Monday the country's parliament unanimously chose Mr Sargsyan for the post, planning to swear him in on Tuesday.

This is the fifth day of protests against what opposition groups are dubbing a "power grab" by the former leader.