LONDON, May 24 (Reuters) - Around 20 people remain in a critical condition after Monday's suicide bombing at a British pop concert, with those wounded battling "highly traumatic injuries" such as damage to major organs and limbs, a health official said on Wednesday.

Twenty-two people were killed late on Monday when a suicide bomber detonated a device packed with metal nuts and bolts as thousands of people streamed out of a concert in Manchester, northern England, by U.S. singer Ariana Grande.

"We are now treating 64 individuals ... of those approximately 20 are receiving critical care, that means very urgent care," Jon Rouse, chief officer for health and social care services in the greater Manchester area, told Sky News.

"There is damage to major organs, major injuries in terms of limbs and some of these individuals are going to need very long term care and support. These are highly traumatic injuries."

(Reporting by Kate Holton, editing by David Milliken) ((kate.holton@thomsonreuters.com; 0044 207 542 8560; Reuters Messaging: kate.holton.thomsonreuters.com@reuters.net))