BEIJING, April 30 (Reuters) - The number of Chinese migrant workers fell by 1.8% in 2020 from the previous year to 285.6 million, according to a survey by the National Bureau of Statistics published on Friday, amid the pandemic that hit the economy. That compared with a 0.8% rise in 2019. A stream of rural workers migrating to cities in search of better jobs and lives has underpinned China’s economic growth and urbanisation in the past four decades. But the pool of cheap labour is steadily drying up as the population ages, pushing up wages amid an economic transformation. The number of migrants working outside their home provinces fell 2.7% to 169.59 million, while those working in their home provinces fell 0.4% to 116.01 million, the survey showed. Of the migrants, 51.5% worked in services sector last year, up 0.5 percentage points from 2019, 27.3% were in the manufacturing sector, and 18.3% were in the construction sector, the survey showed. The average monthly wage of migrant workers grew 2.8% in 2020 from the previous year to 4,072 yuan ($630). That was led by a 3.5% rise for those working in the manufacturing sector. The survey showed the average age of migrant workers stood at 41.4 years, 0.6 years older than the previous year. Workers aged above 50 years old accounted for 26.4% of the total, 1.8 percentage points higher than 2019, the proportion of migrants aged under 40 fell to 49.4% in 2020 from 50.6% in 2019. China’s economy, which slumped in early last year due to the COVID-19 outbreak, grew 2.3% in 2020, the weakest in 44 years. Growth is expected to rebound to over 8% this year.