Citizen journalists reported that thousands of people were trying to flee the besieged city of Homs following an intense bombardment that began at around 7.30pm local time on Sunday.
Avaaz, an international campaigning organisation that co-ordinates a network of local videographers and journalists inside Syria, said that at least 7,000 people were currently trying to escape the embattled west Syrian city, which is home to over 800,000 people and a lynchpin of the ongoing pro-democracy uprising.
Some 2,000 refugees were said to be trapped in the city's suburbs and a further 5,000 on the outskirts of the area of Jobar, where their progress was said to be being blocked by government forces. Roads leading out of the city remain unsafe as they come under sustained attack from the Syrian army.
The districts believed to be under attack on Sunday were named as Sultaniya, Jobar, Kafar Aya, Jouret al Araiss and Baba Amr.
Activists from the group say that they have confirmation from multiple sources. "We have a network of citizen journalists inside Baba Amr and elsewhere in Homs and we also have people outside and around who work in our human supply network who are there tonight", said Avaaz spokesman Alex Renton.
"It looks like the precursor to the ground assault. There's never been shelling on such a scale or over such a wide area of the city," he added.
Syrians voted in a government-sponsored referendum yesterday which, if approved, would allow multi-party elections and time limits on presidential terms. The poll was rejected as farce and a political stunt by activists and Western politicians who say it is designed solely to bolster the beleaguered Bashar al-Assad.
Members of the Syrian opposition called for a boycott and demanded the international community intervene to end a conflict that has left at least 6,000 people dead.
"The Syrian people are calling for international intervention and for this regime to step down," said Omar al-Muqdad, a senior Syrian activist. "They do not want a constitution or political parties. The Syrian government is mocking the international community and the Syrian people."
A new constitution would pave the way for a multi-party system to be established in Syria by abolishing an article that makes the Baath Party the only legal party.