Chief Executive John Lee led officials in observing three minutes of silence, while government vessels honked their horns as Hong Kong mourned the passing of former president Jiang Zemin on Tuesday morning.

All national and regional flags at government premises flew at half-staff as officials watched a live broadcast of the ceremony.

At the Central Government Offices, the CE and his top officials stood in silence to pay respect to the late leader.

Legco president Andrew Leung also led lawmakers to observe three minutes of silence before watching the memorial service in Beijing.

Sirens were heard off the piers in Central at 10am, as government vessels sounded their horns in tribute.

Members of the public also watched the livestreamed memorial service at designated locations set up in all 18 districts.

The Secretary for Home and Youth Affairs, Alice Mak, was at the Kwun Tong Community Centre to watch the ceremony.

"The former president Jiang Zemin, he focused mainly on the welfare of our general public and that is why I choose to come here to watch the live with our residents to remember his contributions to the opening up of our country," she said.

Another mourner at the centre, surnamed Yeung, told RTHK he missed the late president dearly.

"We think he had great achievements. I saw that there were many people mourning him at Tiananmen Square. He deserved all the respect," he said.

All entertainment and celebratory activities organised by the government have been postponed or cancelled.

The Chinese Gold and Silver Exchange also suspended trading for three minutes at 9am, as staff there mourned in silence.