The observatory on Wednesday said Hong Kong was unusually warm last month, with one day seeing the highest March temperature in decades.

The forecaster said March started off cold, but hotter days later on took the mean temperature for the month to 21.1 degrees Celsius, which was 1.6 degrees above the average for that time of year.

"Moreover, the maximum temperature recorded at the observatory reached a record high of 31.5 degrees on March 24, easily breaking the previous record for March set way back in 1973," it said.

The observatory said the higher than usual temperatures were down to a weakened north-east monsoon along the South China coast.

It added that March was also drier than normal, with total rainfall of 21.6 millimetres. That was around 29 percent of the normal figure of 75.3 millimetres, it said.