BEIJING (Reuters) - Profits earned by China's industrial firms grew at their fastest pace in four months in July, aided by a pick-up in sales and reduced costs, the statistics bureau said on Saturday.

Profits in July rose 11.0 percent to 523.01 billion yuan, the National Bureau of Statistics (NBS) said, the fastest growth rate since March.

"Although the growth in industrial profits has accelerated, we still haven't seen an obvious pick up in demand in the market," NBS official He Ping said in a statement accompanying the data.

He said challenges posed to strong industrial profit growth include rising management costs and the costs of tackling overcapacity.

Total profits for the January-July period rose 6.9 percent from the same period a year earlier, compared with a 6.2 rise in the first half of this year.

Profits in the mining sector fell 77 percent from the same period a year earlier while manufacturing profits rose 12.8 percent.

Chinese industrial firms' liabilities at the end of July were 4.5 percent higher than at the same point last year.

The data covers large enterprises with annual revenues of more than 20 million yuan from their main operations.

(Reporting by Sue-Lin Wong; Editing by Simon Cameron-Moore)