HONG KONG/TAIPEI (Reuters) - Singapore is trying to free a shipment of armored troop carriers detained in Hong Kong as they were being shipped home from overseas, Singapore's defense ministry said on Thursday, and Hong Kong authorities said the vessel was from Taiwan.

Singapore authorities were "providing relevant assistance to the Hong Kong Customs and expect the shipment to return to Singapore, expeditiously", the ministry said in a statement.

The Terrex Infantry Carriers and other equipment were delayed on Wednesday in a "routine" Customs inspection after being shipped commercially as with previous exercises, it said.

Taiwanese media said Singapore and Taiwan were in joint drills and a returning military shipment should not have been stopped in Hong Kong, a former British colony that returned to Chinese rule in 1997.

Singapore has a long-established, if low key, military relationship with self-ruled Taiwan, using the mountainous island that Beijing considers a breakaway province for infantry training.

The discovery of equipment used in Taiwanese drills could embarrass Singapore and anger China, which has been distrustful of Taipei since its independence-leaning government came to power in May, regional diplomats said.

China has held out the "one country, two systems" formula under which Hong Kong returned to China as a possible model for Taiwan. Taiwan has not shown any interest.

A statement from Hong Kong's Customs and Excise Department said 12 Singapore-bound containers containing "suspected controlled items" were found in a routine search of a ship from Taiwan.

It noted that licenses and proof of transshipment were needed for certain munitions and weapons, even if they were only in transit.

"Customs officers will take appropriate follow up actions," it said.

(Reporting by J.R. Wu in Taipei, Venus Wu in Hong Kong and Anshuman Daga in Singapore. Writing by Greg Torode. Editing by Nick Macfie)