HONG KONG (Reuters) - Persistent labor shortages, narrowing profit margins and weak orders pose big challenges to Chinese manufacturers and a risk to the government's economic growth target if no additional stimulus is provided, Standard Chartered said on Wednesday.

The bank surveyed 290 Hong Kong-based and Taiwan-based manufacturing companies with operations in China's Pearl River Delta in February and March.

Eighty percent of the respondents expected labor shortages to be at least as bad as last year despite China's slowing economy, while wages were expected to rise 7.7 percent this year.

Wages on average account for more than 20 percent of the total cost base of the respondents, who expected margins to fall by an average of 6.1 percent this year, compared with 0.4 percent last year.

"Lingering high costs, weak orders, narrowing margins and widespread pessimism mean tougher times ahead for an already over-leveraged China Inc, keeping the recovery 'L-shaped' at best," the bank said.

Against this backdrop, the government's aim to reach above an annual 6.5 percent economic growth rate in the next five years looks ambitious in the absence of more policy stimulus, the bank said.

China's working-age population has been declining since 2012 and is likely to keep falling in the coming decades, even with the relaxation of the one-child policy.

(Reporting by Michelle Chen; Editing by Kim Coghill)