DHAKA: China's Foreign Minister Wang Yi has warned against "illegal" protests in Hong Kong, amid major pro-democracy rallies in the territory.

Wang, in Washington, said the matter was an "internal affair" for China.

US counterpart John Kerry urged Hong Kong to handle the protests - seen as a challenge to Beijing - with restraint, reports BBC.

In Hong Kong, students angry at China's plan to vet candidates for 2017 polls have vowed to step up protests if Chief Executive CY Leung does not resign.

They say they will start occupying government buildings if he does not quit by Thursday night.

Overnight, some 3,000 protesters massed outside his office, AFP news agency reports. There is a heavy police presence outside government offices, the South China Morning Post reports.

But the BBC's Juliana Liu in Hong Kong says crowds on Connaught Road in the Central district on Thursday morning were at their lowest ebb since the protest began.

Organisers have attributed this to sheer exhaustion, as the demonstration stretches into its fifth day, she says.

BDST: 1215 HRS, OCT 02, 2014