Another demonstrator has died in protests across Sudan, during the most widespread rallies of anti-government unrest the country has seen.

Key points: An economic crisis triggered protests calling for longtime President Omar Bashir to step down

An economic crisis triggered protests calling for longtime President Omar Bashir to step down Security has used live ammunition to disperse crowds, and hundreds have been arrested

Security has used live ammunition to disperse crowds, and hundreds have been arrested Authorities say 29 have died in protests since December, but rights groups count over 40

The 24-year-old man died from his wounds in Omdurman, a city across the Nile from the capital Khartoum, where crowds were railing against Sudan's three-decade ruler Omar al-Bashir.

That took the official death toll from unrest since December from 19 to 29, according to Government investigatory committee spokesman Amer Mohamed Ibrahim.

Rights groups put the total at more than 40.

Trouble raged into the night in Omdurman, with smoke billowing over a street barricaded by steel poles, burning tyres and tree branches.

In Khartoum, security forces fired tear gas at protesters in various neighbourhoods, witnesses said.

At night, smoke wafted over Khartoum, fires burned and a main street was blocked.

There were also protests in the eastern cities of Port Sudan and al-Qadarif, where hundreds gathered in the main market area, chanting: "Down, that's it! Freedom, freedom."

Triggered by a worsening economic crisis, protests calling for Mr Bashir to step down have spread into the most sustained challenge yet to his rule.

Sudan President Omar al-Bashir has been in power since 1989. ( Reuters: Mohamed Nureldin Abdallah )

One journalist, Zeinab Mohammed Salih, told the BBC that Thursday was the biggest day of protests in living memory.

The opposition Sudanese Professionals' Association, a union group that has led calls for demonstrations, had urged protesters to rally from early afternoon and march to Mr Bashir's palace on the banks of the Nile.

The group said on its social media sites that protesters had gathered in cities including Madani and Sennar, south of Khartoum, as well as smaller towns.

Many protests were reported in Gezira state and witnesses said demonstrators had blocked the main road in al-Nuba district, also south of Khartoum.

Security forces have used tear gas, stun grenades and live ammunition to disperse demonstrations, as well as arresting hundreds of protesters and opposition figures.

According to the BBC, doctors have been increasingly targeted because of their high social standing and role in organising protests.

A member of the Sudan Doctor's Syndicate told the BBC that one doctor who was killed in a protest last week in Khartoum, Babiker Abdulhemeed, had "over 14 live bullets in his body".

State forces also killed a 16-year-old-boy in that protest.

Authorities have blamed the unrest on "infiltrators" and foreign agents, and said they are taking steps to resolve Sudan's economic problems.

ABC/wires