China's plan to dramatically reform Hong Kong's electoral system, expected to be unveiled in a parliamentary session in Beijing starting this week, will upend the territory's political scene, according to more than a dozen politicians from across the spectrum.

The proposed reform will put further pressure on pro-democracy activists, who are already the subject of a crackdown on dissent, and has ruffled the feathers of some pro-Beijing loyalists, some of whom may find themselves swept aside by a new and ambitious crop of loyalists, the people said.

"It will be an earthquake shaking up local political interests," said one person briefed on the impending changes.