SCHAPELLE Corby is likely to spend at least the next five years in an Indonesian jail cell even if the Howard Government strikes a deal with Jakarta for her to be sent home, after the Gold Coast student was sentenced to 20 years in prison for drug-smuggling yesterday.

Three judges in Bali's District Court found the 27-year-old "legitimately and convincingly" guilty of smuggling 4.1kg of marijuana, concealed in a bodyboard bag, into Bali airport in October.

Amid wild scenes in the packed courtroom and as millions watched in disbelief in Australia, three judges found Corby guilty on the primary charge of smuggling drugs.

While they could have sentenced Corby to life behind bars, the judges imposed a lesser sentence after taking into account her age, her good behaviour in the trial and her clean record.

But chief prosecutor Ida Bagus Wiswantanu, who had asked for a life sentence, immediately denounced the sentence as "not enough" and declared he would appeal.

Corby's defence lawyers will also appeal to Bali's High Court, which has 150 days to hear the case from the date it is lodged and can either reduce or increase the sentence, or leave it unchanged.

Corby sobbed and her legs trembled uncontrollably as she stood to hear the verdict and the sentence that followed.

As some locals in the court cheered, Corby, who had wept quietly through much of the hearing, turned to look at her family.

Corby's sister Mercedes, who speaks fluent Indonesian, was the first from her family to comprehend what had happened, yelling from the public gallery that the judges had got it wrong. And as the realisation dawned on the rest of the Corby family, and the rest of the courtroom, the place descended into mayhem.

Her mother Rosleigh Rose repeatedly screamed, "you've taken the word of a liar", referring to the Customs official who told the court Corby was reluctant to open her bodyboard bag.

Hushed by Schapelle's father, Michael Corby, Ms Rose soon broke out again. "Schapelle, we will bring you home," she shouted.

With camera crews leaping in through open windows and with the rest of the public gallery standing on their seats, Corby remained one of the few to retain any dignity.

"Relax, Mum, relax," she said, motioning for them all to sit down. "It's OK, Mum, stop," she said.

Corby's chief defence lawyer, Lily Lubis, said her client was innocent. "She doesn't deserve one day in prison," she said. Despite the sentence, the Howard Government is hoping to secure a prisoner exchange deal with Jakarta so that Corby can serve most of her sentence in an Australian jail.

The three judges dismissed all the defence testimony, including the evidence of Victorian prisoner and accused rapist John Patrick Ford, which they rejected as hearsay. Ford had said he overheard fellow prisoners discussing an airport drug scam, and how Corby had been an innocent dupe. But Judge I Gusti Lanang Dauh said: "The acts of the defendant can damage the mental health of the young generation."

Australian and Indonesian lawyers will resume negotiations on the proposed prisoner treaty early next month.

One sticking point is likely to be whether Indonesia will insist on the remainder of the full 20-year sentence being served in Australia or whether an Australian equivalent sentence taking into account prison remissions is applied.

An Indonesian government spokesman said last night he had heard nothing about a "one-off" prisoner-exchange programme relating to Corby.

Justice Minister Chris Ellison earlier this week said all legal options would be explored in the Corby case including a "one-off" prisoner exchange.

Department of Foreign Affairs spokesman Marty Natalegawa said it would be difficult to justify an agreement relating to a single person. "When Australia came up with this notion of an agreement on a transfer of convicted persons, one of our concerns was that such an agreement, if it's reached, will be of general application," he said. "It hasn't been in our thought processes to have an agreement specific to the case of Ms Corby."

John Howard said that "as a father and a prime minister" he shared the distress of the nation over Corby's jailing.

He said he recognised Australians would be upset by the decision, and that he personally felt sorry for Corby regardless of her guilt or innocence, but he warned it was for the judges, not the Australian public, to make that judgment.

"Now that the guilty verdict has been handed down by the Indonesian court and Ms Corby has been sentenced to a jail term of 20 years, there will be deep feeling in the Australian community," the Prime Minister said. "I recognise that, I say at the outset, that guilty or innocent, I feel for this young woman.

"If she is guilty, I feel for her, that a tragic mistake and tragic act has done so much damage to her young life. If she is innocent, my feelings are redoubled."

Mr Downer urged the public not to let its concern about the conviction spill over into a backlash against Indonesians.

"Indonesian staff should not be threatened, Indonesian government officials should not be abused or threatened," Mr Downer said.

"To do that type of thing is entirely counter-productive."