South Africa's Investec Purchasing Managers Index (PMI) was up slightly in May to 56.4 from 56.2 in April, sponsor Investec said on Tuesday.

"The index remains well above 50, consistent with a sustained expansion in the manufacturing sector," said Andre Roux, head of fixed income at Investec Asset Management.

The April PMI had retreated to 56.2 points after rising to 57.9 in March, its highest level since the first half of 2002. Investec attributed that decline to the fact that the April period had many holidays.

"The April and May readings suggest that the manufacturing recovery strengthened further during the second quarter. It is likely that the improvement in domestic demand remains the strongest driver at this stage," said Roux.

The PMI survey is carried out monthly by the Stellenbosch University-based Bureau for Economic Research in conjunction with the Institute of Purchasing and Supply South Africa.

A reading above 50 in the monthly survey of purchasing managers in the South African manufacturing industry signals expansion, while a reading below 50 means contraction.