Intel has said it is investigating a fire at the company's manufacturing facilities in Arizona that left 13 people injured.

The fire started on Tuesday in a support building handling solvents outside the Fab 22 chip manufacturing site, which is currently under construction, according to Intel spokesman Bill Calder. Reasons for the fire have not been determined and are under investigation, he said.

Five people were sent to hospital for evaluation, but the company declined to comment on the extent of their injuries or medical progress.

Another manufacturing facility in the complex, Fab 32, was evacuated briefly as a precaution. There was no impact to chip production on the sites, and the factories have now returned to normal operation, Calder said.

The company produces millions of chips a year and maintains major manufacturing operations in the city of Chandler, where it has about 9,700 employees. Many chip facilities there are continuously upgraded to make smaller and faster chips for future laptops, desktops and servers.

Both Fab 32 and Fab 22 sites at Chandler are being upgraded to make chips based on the 22-nanometer manufacturing process, which will appear in PCs and servers starting next year. The company earlier this year announced plans to invest more than $5 billion to build a new chip manufacturing facility, called Fab 42, at the Chandler site.

One of the largest chip manufacturers in the world, Intel invests billions of dollars to upgrade factories in order to make smaller and faster chips. Intel maintains chip manufacturing plants in the US, Israel, China and Ireland.