Syrians were summoned to the polls Sunday, to cast votes in a regime-backed constitutional referendum that opposition groups and the West have already dismissed as a farce.

Polls across the country opened at about 7 a.m. local time, but the vote didn't quell the Syrian military's heavy shelling of the flashpoint city of Homs. Activists say at least 29 people were killed there on Sunday alone.

In theory, the referendum on a new constitution could allow for a multiparty system in Syria, which has been ruled by the Baath party for nearly five decades. Critics, however, assert that the vote is just an attempt to mollify President Bashar Assad's opponents.

"Sham votes cannot be a contribution to a resolution of the crisis. Assad must finally end the violence and clear the way for a political transition," said German Foreign Minister Guido Westerwelle.

A new constitution would limit presidential rule to two, seven-year terms. This hasn't won over opposition groups who have demanded Assad's resignation and nothing less.

Speaking from Beirut, CNN reporter Michael Holmes noted that this reform would still permit Assad to stay in power until at least 2026.

"That would still allow al-Assad to rule for another 14 years because it would kick off anew," he told CTV News Channel on Sunday.

Opposition groups including the Syrian National Council and the National Coordiantion Body for Democratic Charge have called for a boycott. Others have called for a strike.

Syrian-based activist Mustafa Osso is among those who are rejecting the vote. In a phone interview, he told The Associated Press that previous gestures masquerading as "reforms" haven't amounted to real change in Syria.

State television has been broadcasting footage of voters heading to the ballot boxes. In Damascus, the country's Information Ministry brought foreign reporters to polling stations to show them the turnout in person.

"It's very difficult to judge dependably and verify independently just how widespread the voting has been," said Holmes.

One voter in the upscale Damascus neighbourhood of Abu Rummaneh said he was satisfied with the reforms proposed in the new constitution, particularly the allowance for party pluralism.

There weren't as many voters, however, in the areas of Rukneddine and Barzeh where demonstrations against Assad have taken place recently. Critics also doubt any voting will be taking place in Homs and the northwestern province of Idlib, where intense clashes have taken place between rebels and security forces.

Roland Paris, an international affairs professor at the University of Ottawa, said he's skeptical of the referendum given the regime's continued violence on voting day.

"Under other circumstances this referendum would be very promising," he told CTV's Question Period on Sunday, adding that the vote is unlikely to make a difference.

Those sentiments were echoed by Canada's former ambassador to Egypt, Ferry de Kerckhove, who said the Baath party is likely to remain an important party in Syria for years to come.

The party took power in a 1963 coup. Seven years later, Assad's father Hafez took power in another coup.

U.S. Secretary of State Hillary Rodham Clinton has urged Syrians involved in the military and business sector to shun Assad.

"The longer you support the regime's campaign of violence against your brothers and sisters, the more it will stain your honour," she said at a news conference in Morocco Sunday.

A solution to the ongoing violence, which has prompted hundreds of thousands of refugees to seek refuge in Jordan, remains unclear.

Russia and China recently vetoed a UN resolution aimed at stopping Assad's bloody crackdown. Western politicians are also divided over the question of whether to arm the rebels or impose even more sanctions.

Activists estimate 7,500 people have been killed since the anti-government uprising began last March.

With files from The Associated Press