ABU DHABI (Reuters) -Saudi Arabia's economy grew 2.8% in the third quarter year on year, preliminary government data showed on Thursday, supported by an increase in non-oil activities.

Non-oil growth rose 4.2%, government activities increased 3.1% and the oil sector grew 0.3%, data released by the General Authority for Statistics showed.

GDP had shrunk in the second quarter on a year-on-year decline in oil activities of almost 9%.

On a quarterly basis, real GDP grew by 0.8%, the statistics authority said.

Growth in the kingdom, the world's top oil exporter, is expected to remain muted this year amid lower oil prices and production which have weighed on government revenue.

A Reuters poll expects the Saudi economy to grow 1.3% this year, a slightly more conservative estimate than the International Monetary Fund's recently revised projection of 1.5%, and among the slowest in the Gulf Cooperation Council bloc.

Oil output is expected to increase next year, driving a rebound in overall economic growth, which will remain supported by non-oil activities.

While Saudi Arabia's public finances remain largely reliant on revenue from hydrocarbons, it has accelerated efforts to bolster non-oil growth and develop new income streams as part of its Vision 2030 strategy.

Non-oil GDP comprises over 50% of overall GDP, and, while there has been some softening in non-oil growth this year, it is still estimated at around 4%, although lower than an average of almost 6% over the last three years.

(Reporting by Rachna Uppal; editing by Eileen Soreng and Jason Neely)