Chief Secretary Carrie Lam Cheng Yuet-ngor said yesterday that government operations could break down if Occupy Central brings the main business district to a standstill.
Her warning came at a meeting with civil service and disciplined services unions ahead of the unveiling of the government's electoral reform report on Tuesday.
Civil Servants General Union chairman Chung Kwok-sing said that at the 1-1/2-hour meeting, Lam "said some political parties might not be satisfied and take action to paralyse Central".
Chung, one of the representatives from eight civil service groups who met Lam, also quoted her as saying she was worried the government might fail to offer services as normal.
Yesterday's meeting was unusual - the last time such talks took place was after a protest-hit visit in 2011 by the then vice-premier Li Keqiang .
Joe Chan Cho-kwong, of the Police Force Council, said Lam warned the political reform report "might have an impact on civil servants, but did not explain why".
The meeting also covered the resources and retirement age of the civil service and filibustering in Legco, Chan said.
He added that Lam expressed support for the police, who were criticised for their handling of protesters after the annual July 1 march for democracy.
The government is due to report on Tuesday on its consultation over reforms for the 2017 chief executive and 2016 Legislative Council polls.
Secretary for Constitutional and Mainland Affairs Raymond Tam Chi-yuen said the reform report would include ideas such as public nomination and party nomination, but would not pass judgment on them.
Views aired in Occupy Central's unofficial referendum and at the July 1 rally - which took place after the consultation ended in May - would be excluded. Lam would brief Legco's House Committee on the report next week, he added.
"It is entirely up to the chief executive to decide whether he wants to reflect the latest sentiments in his own report, to be submitted to the Standing Committee of the National People's Congress," Tam said.
In its report, the government would mention that there were consultation submissions supporting calls to let the public nominate candidates for the 2017 ballot, a source said.
The source said Lam's report would state there was no need to amend the Basic Law to change the method of electing Legco in 2016, as most submissions did not call for major reforms.