HONG KONG remained ahead of Singapore as the busiest container port in January with a 42 per cent year-on-year increase in throughput. According to figures released by the Marine Department yesterday, Hong Kong handled 857,372 TEUs (20-foot equivalent units) in January, up from 603,350 TEUs in January 1992. By comparison, Singapore, which is generally viewed as a fierce competitor, handled 714,000 TEUs in January. Deputy Marine Director Ian Dale said one month was not a realistic base for forecasting annual growth but added the data was encouraging. The 42 per cent growth was achieved despite fewer working days in January because of the Lunar New Year holidays. Apart from the seasonal factor, Mr Dale attributed the growth to the commissioning of two berths at Container Terminal 8 (CT8) and the large increase in river trade. Throughput at Kwai Chung container terminals was up 45.8 per cent to 562,126 TEUs from 385,644 TEUs in January 1992. River trade was up 99.6 per cent to 67,585 TEUs in January. ''This explains only part of the picture,'' Mr Dale said. ''The most important factor is a substantial growth in demand and the port's ability to service that demand.'' Hong Kong handled 9.3 million TEUs last year, retaining its title as the world's busiest container port. Throughput this year is tipped to top 10 million TEUs.