Labor has declared victory in the South Australian seat of Hindmarsh, but has fallen behind in the last undecided seat, Herbert, in Queensland, which may add to the Coalition’s slim majority.

In counting on Wednesday the LNP MP Ewen Jones hit the lead in Herbert for the first time since the 2 July election, leading by 113 votes with 87.2% of the vote counted.

There are still 4,662 votes to count, including 1,363 postal votes and 1,740 declaration pre-poll votes, both of which are favouring the LNP.

If Jones maintains the lead, Herbert would be the 77th Coalition seat, giving it a majority of two in the 150-seat lower house.

At a press conference on Wednesday in Canberra, Malcolm Turnbull said it was “too early to be entirely definitive ... but we are confident, optimistic, that Ewen’s lead will grow as the final thousands of votes are counted”.

He said 77 seats would constitute a “very solid majority”.

Asked about what mandate the government could claim, Turnbull said: “I know that [Bill] Shorten’s attempted victory lap might have misled you but we have actually won the election”.

“That’s the mandate. We have a majority in the House of Representatives.”

Labor claimed victory in Hindmarsh, where the former member Steve Georganas leads by 582 votes. If that result is confirmed it will give Labor 68 seats in the lower house.

At a press conference with the opposition leader, Bill Shorten, Georganas thanked voters and said it was “a great honour and a privilege to be re-elected” to the seat he had represented for nine years before losing in 2013.

Shorten described Georganas as a “fighter” and looked forward to the “hero of Hindmarsh” returning to the Labor caucus.

“I tell you what, people like Steve Georganas make politics worthwhile, because you see true character and true commitment to community,” Shorten said.

Shorten renewed his criticism of the secret Coalition agreement between the Liberal and National parties, which was due to be discussed by Malcolm Turnbull and the Nationals leader and deputy prime minister, Barnaby Joyce, in a meeting on Wednesday.

“I understand that Turnbull and Joyce are meeting in secret to divide up the spoils of government,” Shorten said. “It seems they haven’t learned from the recent election. People do not want politics as usual. They want more transparency.

“I have not heard a single sensible reason for keeping the Coalition deal a secret. This is not internal party business. It is national business and the nation deserves to know what deals are being done.”

Shorten asked how the Australian people could trust the government if it “doesn’t trust the Australian people by revealing the details of a secret Coalition deal”.

Speaking on Sky TV, the major projects and local government minister, Paul Fletcher, described Shorten’s criticism as “a nakedly transparent political gambit”.

“This is mock indignation over the fact the working arrangements between the prime minister and deputy prime minister are not in the form of a public document,” he said.

“Well thank you, Bill [Shorten], we appreciate your advice and we’ll be ignoring it on this occasion.

“All kinds of matters are regularly discussed between very senior political leaders within the Liberal and National parties which are not disclosed publicly.”

He said the deal provided “good and stable government” and there were “good reasons” not to make it public.

Fletcher said Townsville would get $100m for its stadium regardless of whether Jones or Labor’s Cathy O’Toole won Herbert.

“The commitments we have made ... are made to the Australian people,” he said. “They don’t depend on particular outcomes in particular seats.”