An aircraft used by the Thai crown prince has been impounded in Germany due to a dispute over money between Bangkok and an insolvent construction firm, Munich airport said Wednesday.

The Boeing 737 often flown by Maha Vajiralongkorn himself, the heir to the Thai throne, "has been sealed, the doors are not allowed to be opened and it is banned from taking off", airport spokesman Robert Wilhelm told AFP.

Werner Schneider, insolvency administrator for the Walter Bau firm, said that the seizure late on Tuesday followed repeated refusals by the Thai government to pay money it says it is owed.

"We have been trying for years ... to have our justified demands for more than 30 million euros ($42 million) met, and this drastic measure is basically the last resort," Schneider's firm said in a statement.

"The Thai government keeps playing for time and has not reacted to Schneider's demands. Even the involvement of the relevant departments of the German government proved fruitless."

The dispute goes back more than 20 years to the involvement of DYWIDAG, which merged with Walter Bau in 2001, in building a motorway link between Bangkok and Don Muang airport.

After "numerous breaches of contract by the Thai government", Walter Bau, by then insolvent, in 2007 claimed for damages, the legality of which were confirmed by a court in 2009, Schneider said.

"The prince has been regularly coming to Munich for years ... He is probably in Munich right now, in some hotel or other," the spokesman for the airport in southern Germany said.

The Thai embassy in Berlin was not immediately available for comment.