OAXACA (Mexico) (AP) - Tropical Storm Barbara picked up speed on Wednesday and steamed towards a sparsely populated stretch of Mexico's southern Pacific coast, with forecasters predicting it would still reach hurricane strength before hitting land later in the day.

Officials in the southern coastal state of Oaxaca rushed to prepare emergency shelters and suspended classes for schoolchildren in coastal communities as rain began to lash the coast.

Barbara was located about 64km offshore and was moving north-east towards land at about 20kmh, the United States National Hurricane Centre in Miami said.

"We still anticipate that Barbara will become a hurricane in a few hours," the hurricane centre reported.

The stretch of coast east of the port city of Salina Cruz, where Barbara would make landfall, is a largely undeveloped stretch of coastal lagoons, punctuated by small fishing villages. The major oil port of Coatzacoalcos is located on the other side of the narrow waist of Mexico known as the Isthmus of Tehuantepec. But the centre said the storm should weaken rapidly once it hits land, well before reaching Coatzacoalcos.

Mexico issued a hurricane warning for the Pacific coast from Puerto Angel to Barra de Tonala.

Barbara's maximum sustained winds held at around 100kmh, about 14.4kmh short of hurricane strength.

Oaxaca state civil defence director Manuel Maza Sanchez said ports had been closed to navigation in the tourist resorts of Puerto Angel, Puerto Escondido and Huatulco, all located more than 200km to the west.

Rain had begun to fall along the coast on Wednesday, flooding some homes, he said.

He added that classes would be cancelled at schools along the coast for the rest of the week, and that storm shelters were being set up in 20 towns and hamlets.

Such shelters are frequently installed at local schools.