Some oil spill response workers tackling the Gulf of Mexico spill lack the mandatory 40 hours' hazardous materials training, according to the Occupational Safety and Health Administration (OSHA).

In a statement to Bloomberg, the organisation's head David Michaels said reports are coming in that some workers are significantly under-trained.

"We have received reports that some are offering this training in significantly less than 40 hours. This training cannot be shortened," he said.

Responding to the criticism, BP's spokesperson in Houston Daren Beaudo referred calls to the company's Joint Information Centre, but as yet inquiries have yet to be answered.

There are growing concerns about operational standards as the heat index in the region tops 49 Celsius.

BP has this week announced that work to drill relief wells is proceeding ahead of schedule, with the first of the two wells said to be only 300 feet from its target depth.

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