Nine people, including a number of rioters who tried to storm a police station, have been killed in clashes overnight between anti-government protesters and police in Iran, according to state television.

The reports on Tuesday bring the death toll to at least 20 as the protests continue into a sixth day.

The demonstrations - the largest to hit Iran since the protests around the disputed 2009 election - began in Mashhad, apparently over rising food prices, and expanded to several cities.

Hundreds of people have been arrested, including 450 people arrested in Tehran over three days, according to a report by the semi-official ILNA news agency.

In the latest development, state TV reported that six rioters were killed during an attack on a police station in the town of Qahdarijan when they tried to steal guns from the facility.

In the town of Khomeinishahr, an 11-year-old boy and a 20-year-old man were killed, state TV said.

A member of Iran's paramilitary Revolutionary Guard was also reported killed in the town of Najafabad.

It was unclear if this was the same fatality as that reported by Iran's semi-official Mehr news agency on Monday.

Mehr reported a gunman had killed a policeman and wounded three other officers during a protest in the same location - the fist reported fatality among Iran's security forces.

Iran's President Hassan Rouhani has acknowledged the public's anger over the flagging economy, but he has also warned that rioters and looters will be arrested.

That was echoed Monday by judiciary chief Ayatollah Sadegh Larijani, who urged authorities to confront rioters, state TV reported.

"I demand all prosecutors across the country to get involved and the approach should be strong," he said.

US President Donald Trump, meanwhile, has weighed in on Twitter apparently in favour of the protesters saying it is "time for change" in Iran.