HONG KONG, Jan. 22 (Xinhua) -- The government of the Hong Kong Special Administrative Region (HKSAR) has expressed grave grievance over the death of three on-duty Customs officers and extended the deepest condolences to their families.

Five Customs officers fell to the sea as their vessel capsized after ramming an unknown object during a patrol at the waters near Sha Chau around 9 p.m. local time on Tuesday. Three of them were certified dead after being sent to hospitals, and the other two were injured.

The cause of the incident is under investigation.

"I am profoundly grieved by the unfortunate loss of three Customs colleagues who were on duty last night and I offer my deepest condolences to their families," said the HKSAR Chief Executive Carrie Lam, who is currently on duty visit in Davos, Switzerland, adding that she hopes the injured officers would recover soon.

She promised that the Civil Service Bureau and the Customs and Excise Department of the HKSAR government will make every effort to support the families.

The Liaison Office of the Central People's Government in the HKSAR on Wednesday also expressed deepest sorrow over the death of the Customs officers and offered condolences to their family members and sympathy to the other injured officers.

The office said it will do its best to provide assistance if the HKSAR government has any needs.