A hurricane watch has been issued for a portion of Mexico's coast as Tropical Storm Barbara approaches in the Pacific.

The hurricane watch early Wednesday covers an area in the Gulf of Tehuantepec from Puerto Angel to Barra de Tonala.

A tropical storm warning is in effect for the area between Puerto Angel and Boca de Pijijiapan.

Barbara's maximum sustained winds have increased to near 95 km/h. The U.S. National Hurricane Center in Miami says additional strengthening is likely and the storm could be near hurricane strength before it makes landfall.

The storm is centred about 160 kilometres south-southwest of Salina Cruz, Mexico, and is moving northeast near seven km/h.