Government tanks and armoured vehicles have deployed in Hama, where heavy gunfire has been heard and at least four people have been wounded, Syrian activists say Al Jazeera reported
The new violence in Syria's fourth-largest city comes amid a violent military campaign in nearby Homs, one of the focal points of the country's eight-month uprising.
The fighting in Homs, which entered its sixth day on Tuesday, has left more than 110 people dead, according to anti-government activists with the Local Co-ordination Committees. Two people died there on Tuesday, they said.
An eight-year-old girl had been shot dead by a sniper in Hawla, in Homs province, and that a 27-year-old man had been killed in Bayada, in Tartous province, according to the London-based Syrian Observatory for Human Rights.
Activists reported that at least 11 people were killed across the country on Monday, including two children.
In Hama, around 50km to the north, snipers and government militias surrounded a medical complex and the headquarters of the ruling Baath Party, the LCC said.
Tanks and armoured vehicles could be seen moving toward the city centre, and four people had been wounded in the Sharqiyya area, the activists said. Explosions and heavy gunfire could be heard in the city, and electricity and internet services had been disabled, they said.
The opposition Syrian National Council, based in Turkey, has called for international intervention in Homs, which it described as a "humantarian disaster area".
At least 3,500 people have died since major protests first broke out in Syria in March, the UN said on Tuesday.
A large portion of the population, including businesspeople and minorities, remain loyal to the government of President Bashar al-Assad, who has been in power for 11 years.
Assad's family, which has governed Syria since 1971, belongs to the minority Alawi sect of Shia Islam.
In recent weeks, violence between government forces and armed opposition groups appears to have risen, especially in Homs. Video posted on YouTube on Monday shows armed men in camouflage military uniforms marching in the city, Syria's third-largest, proclaiming themselves defectors to the "Syrian Free Army".
In the video, one fighter calls for a no-fly zone and says that the uprising against Assad is peaceful.
The ongoing violence comes despite a ceasefire plan announced by the Arab League in Cairo on November 2. In response to the continued fighting, the Arab League has called for an emergency meeting on Saturday.
The League said that the meeting was called because of "the continuation of violence and because the Syrian government did not implement its commitments in the Arab plan to resolve the Syrian crisis".
Sheikh Hamad bin Jassim Al Thani, the Qatari prime minister and chair of a panel on the crisis, has said that "if Syria does not respect its commitments, the ministerial committee will meet again and take the necessary decisions".
The Arab roadmap called for an end to violence, the release of those detained, the withdrawal of the army from urban areas and free movement for observers and the media, as well as talks between the regime and opposition.
Al Jazeera's Rula Amin, reporting from neighbouring Lebanon, said: "People there are trying to tell the government that they will not succumb and they will continue to protest until they topple the regime...despite the heavy presence of the security forces."
In a statement released on Monday, the Syrian National Council urged the UN, the Organisation of Islamic Co-operation and the Arab League to act "to stop the massacre committed by the regime".
It also called on the international community to send "Arab and international observers, instantly, to the city of Homs to oversee the situation on the ground, and prevent the regime from continuing to commit brutal massacres".