NEW DELHI — A powerful cyclone sweeping through southern India has killed at least 21 fishermen and stranded more than 90 others at sea, according to a government official in the state of Kerala.

The storm, Cyclone Ockhi, caught many fishermen off guard over the weekend after it formed quickly in the Arabian Sea and began lashing the Lakshadweep Islands and coastlines in the states of Kerala and Tamil Nadu.

On Monday afternoon, the cyclone was about 480 miles southwest of Surat, a city in Gujarat State. The storm was expected to hit the coast near Surat by Tuesday evening, and lose some of its intensity.

The extent of the damage was still unclear on Monday, but Mohammed Faizal, a member of Parliament representing Lakshadweep, said the losses from damage on the islands exceeded $77 million.