Potential candidates that the central government does not want on the ballot will be screened out by a nominating committee on national security grounds.

The HKU student union said they hoped to raise awareness of the importance of democracy with the strike, which is expected to be a precursor to acts of civil disobedience.

The declaration demands that the central and local governments offer a democratic plan for the 2016 Legislative Council elections and the 2017 chief executive vote. It calls for the public to be allowed to nominate candidates in 2017 and for all Legco seats to be directly elected in 2016.

As it stands 35 of 70 Legco seats are democratically elected.

The declaration also calls on lawmakers to veto any official plan for the 2017 election which fails to comply with international standards on universal suffrage.

The union urged all teachers to support the students by not penalising them for their absence, but to arrange catch-up tutorials sessions and even to join the strike.

“In times of crisis when truth is distorted, our school motto “Sapientia et Virtus” [Wisdom and Virtue] reminds us to cling onto justice and to stand up for virtues we truly treasure,” the statement said.

On Tuesday a department head at Chinese University said Occupy Central would be a legitimate reason to miss classes. Professor Gordon Matthews said he will provide filmed lectures to help students who join class boycotts in protest at Beijing's restrictive framework for the city's political reform.

"Students miss classes from time to time. This is better than going to Lan Kwai Fong and getting drunk, after all," Professor Gordon Mathews, head of the anthropology department at the university, told the .

"I would want people to be in tutorials … but if someone were to miss some tutorials because they were occupying Central, I think that will be a legitimate reason and I might not penalise students for that," he said.

Mathews' remarks came as the city's first chief executive, Tung Chee-hwa, opposed the school strikes initiated by the Hong Kong Federation of Students and student-led group Scholarism which could take place in mid-September.

Mathews said that putting filmed classes online would be a way to help the student activists.

"That means if students were to miss a few classes, it would not be a great deal," the anthropologist said, adding that it would be up to individual teachers to decide how to deal with the issue.

Other academics expressed similar views.

Professor Timothy O'Leary, head of the University of Hong Kong's school of humanities, told the the school had issued guidelines advising teachers to be "as flexible as they can be" during the boycott to minimise the impact on students' learning.

That included rescheduling compulsory tutorials and avoiding deadlines for papers during the period. "We would not condemn students as we understand what they are doing."

In contrast, Baptist University - which did not encourage students to join class boycotts - said students absent without approval for more than 15 per cent of scheduled classes of a subject would be banned from exams.

Mathews, who has lived in Hong Kong since 1994, also pointed out the dilemma expatriates faced amid the political tension.

Deeply disappointed by the national legislature's Sunday decision that effectively ruled out pan-democrats running for chief executive in 2017, Mathews said he feared his participation in Occupy Central would bring harm to the movement.

"Hong Kong is my home … I would never want to be a coward here," he said. "But I would hate to be used by China."

This could happen through Beijing saying his attendance showed American interference in the democracy movement.

Mathews said the best solution for him was going at scene to support Occupy Central, but avoid being arrested. The movement’s co-organiser Dr Chan Kin-man also told Mathews that he was more than welcome to join the protest after he raised the concerns.