Protesters stormed Libya's state broadcaster and torched police stations in Tripoli as Muammar Gaddafi's son warned that the Arab world's longest ruling leader would fight to the death to retain power on Monday.

Barely a week after his neighbour Hosni Mubarak was forced out of the presidency in Cairo, the challenge to Gaddafi's 41-year rule reached the Libyan capital with witnesses reporting several mainstays of the regime had been overrun.

The President of Yemen, another ruler who has chalked up more than three decades in power, faced growing calls to quit despite his insistence that he would only exit via the ballot box.

And a top exiled opposition figure said he planned to return to Bahrain, providing fresh impetus to the pressure for the island's ruling family to implement wide-ranging reform.

While there was fresh violence in several Arab cities, the most dramatic events were in Tripoli where the sound of heavy gunfire broke out in downtown areas for the first time since the uprising began in eastern Libya last week.

Although government restrictions have complicated the task of compiling a list of casualties, Human Rights Watch said the death toll was at least 233 since last Thursday.

Libya's Al-Jamahiriya television and Al-Shababia radio were both forced to halt broadcasts on Sunday evening after their offices were ransacked and looted, according to witnesses.

Although they did manage to resume broadcasts on Monday, a number of witnesses said protesters had torched other public buildings in the capital overnight, including police stations and offices of the governing People's Committee.

The People's Conference Centre in Tripoli's residential neighbourhood of Hay Al-Andalous - which regularly hosts pro-regime demonstrations and official meetings - was also set alight, a resident who lives nearby told AFP.

Al-Jamahiriya 2, the second state television channel, and Al-Shababia were launched by the Libyan leader's influential son Saif al-Islam in 2008 and later nationalised when broadcasting was declared a state monopoly.

While his 68-year-old father has yet to address the nation since the unrest erupted last week, Saif al-Islam took to the airwaves on Monday to condemn the uprising as a foreign plot that would be crushed.

"Libya is at a crossroads. If we do not agree today on reforms... rivers of blood will run through Libya," he said in a fiery but rambling speech.

"We will take up arms... we will fight to the last bullet. We will destroy seditious elements. If everybody is armed, it is civil war, we will kill each other... Libya is not Egypt, it is not Tunisia."

But his insistence that the regime would not be the next in north Africa to crumble in the face of a popular revolt did not convince those in Tripoli.

"We can hear gunfire outside. It hasn't stopped all day," a resident of a suburb east of Tripoli told AFP by telephone.

"When we heard the unrest was approaching, we stocked up on flour and tomatoes. It's definitely the end of the regime. This has never happened in Libya before. We are praying that it ends quickly."

Foreigners were taking flight from the unrest, with Norwegian energy giant Statoil saying it had begun evacuating non-Libyan staff working in the country.

In London, British energy group BP said it too was making preparations to evacuate some of its staff from Libya, where it employs 140 people, including around 40 foreigners.

Yemeni President Ali Abdullah Saleh, head of the region's second longest-running regime, also struck a note of defiance in a press conference which was held against a backdrop of a growing clamour for his departure.

"If they want me to quit, I will only leave through the ballot box," Saleh told a news conference as protesters, including opposition MPs, gathered outside Sanaa University.

"The opposition are raising the level of their demands, some of which are illicit," the Yemeni leader said.

In the country's south, police shot dead a protester in the regional capital, Aden, where protests have raged killing 12 people and wounding dozens since February 16, medics and witnesses said.

While Yemen is the poorest Arab country, some of the region's wealthiest countries have also been caught up in the wave of unrest.

In Bahrain, where a mainly Shiite population has long chafed against being ruled by a Sunni royal family, protesters were gearing up for a rally they hoped would bring tens of thousands to the central Pearl Square.

Ahead of the rally, Hassan Mashaima, leader of Bahrain's opposition Haq movement, told AFP he would return to Manama on Tuesday, despite having the threat of terrorism charges hanging over him.

In a telephone call from his base in London, Mashaima said he had "no guarantees" he would not be arrested on arrival.

"But under the current circumstances, I cannot remain outside my country," he added.