The court convicted them of possessing half a kilogram of methamphetamine, which they have denied since they were arrested at sea near the popular tourist resort of Subic in July 2016.

“A few days ago, Foreign Minister Wang Yi said China would pay great attention and seriously follow up should Chinese nationals suffer unfair treatment overseas,” Lam said on Saturday.

“The Hong Kong government will also definitely provide assistance to Hongkongers facing difficulties abroad.”

She did not specify what steps her administration would take.

Wang had been speaking in relation to the case of Sabrina Meng Wanzhou, chief financial officer of Huawei Technologies, who was arrested in Canada at the behest of the US over allegations she sold telecoms equipment to Iran, in breach of sanctions.

Lam said she would actively follow the case, as she did the case of another Hongkonger, Tang Lung-wai, four months ago.

“We have actively followed up on the case of another Hongkonger who got into trouble in the Philippines. And I am personally willing to follow up on the four Hong Kong men’s case with the same attitude,” she said.

She added that the quartet’s case had been referred to the Security Bureau, which sought to meet the families. She said the administration would focus on fair trials and humane treatment for the affected city residents.

“Yet I can’t directly intervene in the judicial system and procedures of foreign countries,” she added.

Lam wrote to Philippine President Rodrigo Duterte In August to ask for “compassionate consideration” in expediting a request to the Philippine Bureau of Immigration so Tang could receive a “fair and just trial”.

Tang, 47, was arrested in the Philippines in 2000, and has been jailed for 18 years after being found guilty of possession of methamphetamine.

His ordeal took a surprising turn after Lam’s letter in August. Philippine immigration authorities released a critical piece of evidence and Tang launched a final appeal.

The four men in the more recent case – Lo Wing-fai, 44, Chan Kwok-tung, 31, Kwok Kam-wah, 49, and Leung Shu-fook, 51 – were detained aboard a 50-metre fishing boat about 3km off the coast of Zambales province, northwest of Manila, in an operation led by then Philippine police chief Ronald dela Rosa.

The arrests came at a time of high tension over territorial claims in the South China Sea and a pledge by Duterte to wage a “relentless and sustained” war on drugs and crime.

Authorities said the men were part of a racket smuggling drugs to mainland China, but the families complained it was a set-up. The men’s relatives said officers found nothing in an initial search but later claimed to have discovered the drugs in one man’s backpack, which had been taken from the men’s sight for a few minutes. The defence suggested during the trial that the drugs were planted in the bag.

Chief Secretary Matthew Cheung Kin-chung said on Saturday afternoon whether the central government would intervene depended on the case’s development.

“The Hong Kong government is highly concerned about the case and will seriously follow up on it,” Cheung said. “The Immigration Department has visited the four men several times through the Chinese embassy in the Philippines. The government will continue to keep an eye on the case through China’s foreign ministry and central government.”

A spokesman for the Security Bureau said Secretary for Security John Lee Ka-chiu would contact China’s foreign affairs commissioner in Hong Kong in person and write to the Philippine consulate in the city to urge a fair trial and protection of the prisoners’ legal rights.

The Immigration Department also asked China’s embassy in the Philippines to help arrange consular visits, according to the spokesman.