Lawyers for embattled South Korean President Park Geun-hye struck a defiant note on Friday, saying a parliamentary vote to impeach her had no legal basis and should be overturned by the Constitutional Court.

Park was indicted in a Dec. 9 vote by a wider-than-expected margin of 234 to 56, setting the stage for her to become the country's first democratically elected leader to be ejected from office.

"We see no grounds for impeachment and it should be struck down," Lee Joong-hwan, a former prosecutor who is part of the team representing Park, told reporters at the court building where her fate will be decided.

In their first comments since the impeachment vote, Park's lawyers also said it was unlikely she would appear before the court when it begins hearing the case.

The court has up to 180 days from last Friday's impeachment vote to reach a decision.

Park, 64, whose father ruled the country for 18 years after seizing power in a 1961 coup, is accused of colluding with long-time friend Choi Soon-sil, who has been indicted and is in custody, to pressure big businesses to make contributions to non-profit foundations backing presidential initiatives.

Park, who is serving a single five-year term set to end in February 2018, has denied wrongdoing but apologised for carelessness in her ties with Choi.

She has refused widespread calls to resign immediately, despite huge weekly protests and parliament's overwhelming vote for impeachment, fuelling concern the political crisis could drag on for months.

Another rally is expected on Saturday, while a pro-Park demonstration is also scheduled.

The legal team is looking to move quickly, her lawyer said.

"We want a quick process and will not request to delay it," Lee said.

Although stripped of her presidential powers, which are being wielded by the prime minister, Park retains her title and her official residence.

She has presidential immunity while in office, but risks facing prosecution upon her departure.

Hundreds of people entered a lottery for one of the 80 seats available to the public on Choi's first day of trial on Monday, with one winner cheering in celebration after picking his number out of a plastic box at the Seoul Central District Court.

Earlier, an official in the presidential Blue House had said parliamentary investigators would not get access to Park's official residence, citing national security.

"They can't come inside," the official, who declined to be identified, told reporters.

"We haven't changed our stance on that. We are in talks regarding where to meet, and what to do, if parliament's special committee wants to hold an inspection."

The official also denied allegations the Blue House had ordered South Korea's intelligence agency to spy on judges, including the chief justice of the Supreme Court.

"The Blue House has never spied on anybody and it's something that should not happen," the official said of the allegations, aired in a televised parliamentary hearing on Thursday.

On Friday, Lee Kyu-chul, a spokesman for the special prosecutor, told reporters the team would keep looking for legal grounds allowing it to enter the Blue House.

The special prosecutor's office has said it wants to search the offices of indicted former Blue House officials.

The fallout from the impeachment vote continued to threaten the survival of Park's Saenuri Party, many of whose members had voted against her, with party leader Lee Jung-hyun, a staunch supporter of the president, resigning on Friday.

The party had been divided between the pro-Park faction and those blaming her for declining public support for the conservatives, who lack a clear candidate for the next presidential election.

A new poll has to be held in 60 days if Park is removed from office.