MEXICO CITY (REUTERS) - Tropical Storm Barry, the second of the Atlantic hurricane season, strengthened as it churned towards Mexico on Wednesday, threatening to bring heavy rains to oil and power installations near the country's Gulf coast.

The Minatitlan oil refinery of state oil monopoly Pemex and the Laguna Verde nuclear power plant, both in Veracruz state, are being monitored closely, said Noemi Zoila, head of the local government's emergency services.

Mexico's three major Gulf coast oil export terminals - Coatzacoalcos, Cayo Arcas and Dos Bocas - closed on Wednesday because of heavy rain and reduced visibility.

Barry was about 60 kilometres east-northeast of the port of Veracruz, moving at 9 kph as it approached land, the US National Hurricane Center said.

The storm's maximum sustained winds were 75 kph, the centre added, and a tropical storm warning was in effect along a costal stretch from Tuxpan to Punta El Lagarto.

The biggest impact was expected to be felt in southern and central parts of Veracruz state late on Wednesday and early on Thursday, said local emergency services spokesman Manuel Escalera.

Mr Escalera added that the storm could cross Pemex's installations as well as hydroelectric dams. He said the state was prepared to offer temporary shelter to up to 500,000 people, and that all public schools would be closed on Thursday as a precautionary measure.

The first tropical storm of the 2013 Atlantic Hurricane season, Andrea, formed in the Gulf of Mexico on June 5 and moved toward Florida, Georgia and North Carolina.