A Thai court has extended the pre-trial detention of a law student who shared a BBC profile of King Vajiralongkorn, despite an outcry from academics and a dramatic protest from his mother inside court.

Jatupat Boonpattararaksa, better known as "Pai" (bamboo), was one of more than 2,000 people to post the profile to Facebook, but the well-known activist was the only one to be arrested.

He faces 15 years in jail if found guilty, in a case seen as a test of how Thailand's strict lese majeste law will be applied under the new king.

The Khon Kaen provincial court considered the police application to extend Jatupat's 10-day detention for a sixth time.

When the judge announced the hearing would be conducted in secret — for the purpose of "maintaining peace and order" — Jatupat's mother reportedly stood up, shouted that she would trade her life for justice and ran into a wall, sustaining minor injuries.

The arrest of Jatupat and his lengthy remand have been criticised.

"[Human Rights Watch] thinks that the extending of detention seems to be upfront punishment for [lese majesty law] 112 before the court hears whether the accused is guilty or not," tweeted Sunai Phasuk, senior researcher on Thailand for the US-based rights group.

Jatupat's lawyer said he would make another bail application. An earlier appeal to allow the student to sit his final law exam in December was also denied.

Jatupat's political activism has rankled Thailand's military Government.

Months after the 2014 coup, he and other students interrupted a speech by Prime Minister General Prayut Chan-o-cha to flash a three-fingered salute — a symbol of defiance copied from the Hollywood movie The Hunger Games.

Jatupat Boonpattararaksa's mother protested after the judge's ruling the hearing would be conducted in secret. ( Supplied: Facebook )

'Decline of rule of law'

Jatupat was initially released on bail in December, but was rearrested on the basis of allegedly mocking the court and not deleting the BBC profile from his Facebook page.

The alleged disrespect appeared to stem from photos posted online of Jatupat and friends celebrating outside the Khon Kaen court, which academics have pointed out was not illegal and was not restricted by his bail conditions.

Student activist 'Pai', centre in black top, celebrates his bail with friends outside the Khon Kaen court. ( Facebook )

An open letter signed by 352 members of the Thai Academic Network for Civil Rights said the student's legal rights had been violated and the case was an example of the "decline of the rule of law".

"Deriding state power or expressing no fear of the law shall not be a base for the decision to deny bail," the letter stated.

The scholars criticised "double standards" in courts and decisions that had questionable legal basis.

"Such problems seemed progressively more serious after the NCPO staged the coup d'etat, when laws were exploited to curb the freedom of civilians whose views differ from the power holders," the academics wrote, using the formal name for Thailand's military junta, the National Council for Peace and Order.

11 years' jail for online messages

In a separate case last week, a 28-year-old man was sentenced to 11 years and four months' imprisonment for lese majeste and computer crimes.

Burin Intin pled guilty to insulting the monarchy in two messages posted online, one in a comment to a video and another in a private chat with another person.

The nature of his comments was not known and likely could not be published by the ABC, which must self-censor its reporting on royal issues in order to keep the Bangkok bureau open.

The other party in the chat, Patnaree Chankij — the mother of another well-known pro-democracy activist — was also charged with lese majeste.

Her charge is based on a single word — her response of "ja", which is a Thai term to acknowledge that something has been said.

Patnaree will face court in March.