Hong Kong customs found cocaine worth HK$246 million (US$31.7 million) hidden in an aircraft engine shipped from South America, in its biggest seizure of the drug so far this year.

The engine was inside a shipping container that arrived from Ecuador in March, but the haul was only discovered last week after it was opened for inspection at Hong Kong International Airport. Officers found 217kg of cocaine hidden inside.

Customs officers were suspicious as jet engines were rarely shipped to Hong Kong from South America and the consignee never collected the cargo.

An X-ray of the engine revealed an unusual shape and personnel from the Government Flying Service (GFS) were called in to inspect the machine at the Kwai Chung cargo examination compound last Tuesday.

“It is an old and unserviceable engine,” said Benson Lee Tak-shun, head of Ports and Maritime Command.

Raymond Ho Wai-ming, a GFS manager said the engine was rusty, but the outer shell of the combustion chamber had been spray painted to make it look new.

Officers had to drill a hole on the surface of the chamber and then used a borescope to check.

“A lot of common engine components were not found in the chamber so we suspected it was used for another purpose,” Ho said.

The machine was then taken to the GSF headquarters at the airport, where it was broken open for inspection on Wednesday.

Superintendent Barry Chu Yin-min, from Customs Drug Investigation Bureau, said after breaking open the machine, a secret compartment was found inside the combustion chamber.

“Eight tailor-made containers were found in the chamber. Inside the containers were 217 slabs of cocaine. Each slab weighs 1kg,” he said.

Chu said he believed some of the drugs were for local consumption, but most of the haul was destined for other countries.

“This is the city’s largest seaborne cocaine trafficking case since 2012,” he said. “It is also the first drug trafficking case where we found illegal drugs concealed in an aircraft engine.”

Chu said the consignee in Hong Kong was a trading company which was set up in April last year through a local secretariat firm.

Customs officers were still searching for its male director and a female employee in connection with the case. As of Tuesday afternoon, no one had been arrested.

The city’s biggest cocaine seizure to date was made in 2012 when customs officers found 649kg of the drug worth HK$760 million hidden in a shipping container that arrived from Ecuador. The seizure was made following a tip-off from the United States Drug Enforcement Administration (DEA).

According to official statistics, Hong Kong authorities confiscated 1.3 tonnes of cocaine last year, up nearly 145 per cent from the year before. According to police, last year’s haul was the biggest since records began in 2003.

More than 30 per cent came from a major bust of a Balkan drug cartel by customs officials working with the DEA and the European Union Agency for Law Enforcement Cooperation.

The operation – code-named “Familia” – started with Hong Kong officers arresting five men and seizing 421kg of cocaine in three cases in April. Authorities believed most of the drugs were supposed to be smuggled to Australia by a private jet.

Another 11 members of the cartel, including the alleged ringleader, were detained in Croatia, the Czech Republic, Serbia and Switzerland in May.