Fire and gunshots have erupted at Tehran's notorious Evin prison tonight, an Oslo-based rights group has reported, as the protest movement sparked by Mahsa Amini's death in custody enters its fifth week.

Flames and a plume of smoke could be seen billowing into the sky and pops of what appeared to be gunfire could be heard in video footage shared by Iran Human Rights on Twitter.

"A fire is spreading in Evin prison" and an "explosion was heard" from the facility, the 1500tasvir social media channel that monitors protests and police violations said on Twitter.

Angry demonstrators took to streets across Iran again today despite internet cuts, as the protest movement sparked by Ms Amini's death in custody entered a fifth week.

The 22-year-old died on 16 September, three days after falling into a coma following her arrest by Iran's notorious morality police for an alleged breach of the Islamic republic's strict dress code for women.

Young women have been at the forefront of the biggest wave of street protests seen in the country for years.

"Guns, tanks, fireworks; the mullahs must get lost," women without hijabs chanted at a gathering at Tehran's Shariati Technical and Vocational College, in a video widely shared online.

There have been protests across Iran over the death in detention of Mahsa Amini

Scores of jeering and whistling protesters hurled projectiles at security forces near a landmark roundabout in Hamedan city, west of Tehran, in footage verified by AFP.

Despite what online monitor NetBlocks called a "major disruption to internet traffic," protesters were also seen pouring onto the streets of the north-western city of Ardabil, in videos shared on Twitter.

'Brave women of Iran'

Shopkeepers went on strike in Amini's hometown Saqez, in Kurdistan province, and Mahabad in West Azerbaijan, said 1500tasvir.

They were responding to an appeal for a huge turnout for protests on Saturday under the catchcry "The beginning of the end!"

"We have to be present in the squares, because the best VPN these days is the street," activists declared, referring to virtual private networks used to skirt internet restrictions.

A call went out this week for "retirees" of the Revolutionary Guards to meet today given "the current sensitive situation", according to a journalist at Shargh newspaper.

At the gathering, a guards commander said three members of its Basij militia had been killed and 850 wounded in Tehran since the start of the "sedition", state news agency IRNA said.

The women-led protests have won support from the US president.

"I want you to know that we stand with the citizens, the brave women of Iran," Joe Biden said late last night.

"It stunned me what it awakened in Iran. It awakened something that I don't think will be quieted for a long, long time."

At least 108 people have been killed in the protests, and at least 93 more have died in separate clashes in Zahedan, capital of the southeastern province of Sistan-Baluchestan, according to Oslo-based group Iran Human Rights.

The unrest has continued despite what Amnesty International has called an "unrelenting brutal crackdown" that has included an "all-out attack on child protesters" -- leading to the deaths of at least 23 minors.