Hong Kong (CNN Business) China's economy grew at its slowest pace in almost three decades last year.

The world's second biggest economy expanded 6.6% in 2018, according to official data published Monday. That's the weakest annual performance since 1990.

Chinese growth has lost momentum following government efforts to try to rein in high levels of debt. It has also started feeling the effects of the trade war with the United States , which has resulted in new tariffs on more than $250 billion of Chinese exports.

The deteriorating situation in a market that businesses around the world rely upon for growth is having a widespread impact. It has spooked investors and prompted warnings from top companies like Apple ( AAPL ).

Economic growth in China slowed to 6.4% in the fourth quarter of last year, according to Monday's data, in line with economist's predictions.