Yesterday's resignation by Tsang Yok-sing is the second time the DAB chairman has offered to quit - the first time was shortly after the July 1 march.
It is understood that Mr Tsang informally tendered his resignation to core members of the DAB after an estimated 500,000 people took to the streets to protest against the national security legislation.
'Mr Tsang said he should bear responsibility for the fallout of the July 1 march because the party leadership supported the legislation,' a source said.
But the source said the idea was not discussed at any formal party meeting and some core members said there was no need for Mr Tsang to quit.
DAB secretary-general Ma Lik said that by noon on Sunday the party leadership expected the party would suffer a severe blow at the polls.
Mr Tsang chaired an emergency meeting of his party's central committee which started at 1.30am yesterday as the results started rolling out.
