Abdo Hussameldin, Syria's deputy oil minister, has announced his defection in a video posted by activists on YouTube.
If confirmed, Hussameldin would be the highest ranking civilian official to abandon President Bashar al-Assad since the uprising against his rule erupted a year ago.
"I, Abdo Hussameldin, deputy oil and mineral wealth minister in Syria, announce my defection from the regime, resignation from my position and withdrawal from the Baath Party. I join the revolution of this dignified people," Hussameldin said in the video.
The authenticity of the video could not be immediately confirmed by Al Jazeera.
Rami, the activist who shot the video and posted it on YouTube on Thursday, told the AFP news agency in Beirut that the opposition helped arrange his resignation. He asked that the location where the video was shot not be disclosed for safety reasons.
Hussameldin denounced Russia and China for backing the regime, saying they were not "friends of the Syrian people but partners in the killing of the Syrian people".
He said he had served in the Syrian government for 33 years and did not wish to end his life "serving a criminal regime".
"That is why I have joined the right path, knowing that this regime will burn down my house, hunt down my family and fabricate lies," he said.
He advised his colleagues to abandon "this sinking ship".
According to the United Nations, more than 7,500 people have died in the government crackdown to put down the revolt that eruped last March.
"I say to this regime: you have inflicted on those who you claim are your people a whole year of sorrow and sadness, denying them basic life and humanity and driving Syria to the edge of the abyss," Hussameldin said.
Assad appointed Hussameldin, 58, to his current position through a presidential decree in 2009. On Wednesday, Hussameldin said the country's economy was "near collapse". There was no mention of the defection on Syrian state media.
Wearing a suit and tie, Hussameldin looked relaxed as he looked directly into the camera in a tight head and shoulders shot, appearing to read from a prepared statement on his lap as he sat on a dark grey chair against a yellow background.
Opposition sources say the government, controlled by Assad's minority Alawite sect that has dominated power in Syria for the past five decades, has effectively stopped functioning in provinces that have been at the forefront of the uprising, such as Homs and the northwest province of Idlib.
The news of the ministerial resignation came hours after US defense secretary Leon Panetta said Washington was looking at delivering non-lethal aid to Syria's rebels, hinting at the first direct US assistance to forces seeking Assad's downfall.
On Wednesday, Russia accused Libya during a UN Security Council meeting of running a training centre for Syrian rebels.
The accusation came on the day the UN humanitarian affairs chief, Valerie Amos, briefly visited the opposition neighbourhood of Bab Amr in Homs.
Amos followed a delegation from the Syrian Arab Red Crescent into the district, after first receiving approval from the government, said Saleh Dabbakeh, a spokesman for the International Committee of the Red Cross, told Al Jazeera.