At 1200 GMT, Pamela crossed on to land about 65 kilometers (40 miles) north of the Pacific port of Mazatlan, in the northwestern state of Sinaloa, with sustained winds of 120 kph (75 mph) and was moving at 22 kph (14 mph), according to data from the Miami-based NHC.

The "center of Hurricane Pamela was making landfall on the west-central coast of Mexico near Estacion Dimas," a community of about 3,600 inhabitants, the NHC reported.

The storm had initially been forecast to hit as a major hurricane -- above a Category Three on the Saffir-Simpson scale of five -- but weakened as it approached the coast and was even briefly downgraded to a tropical storm.

It is expected to weaken again as it moves over land.

In Mazatlan, 16 US citizens were in shelters after being stranded at the local airport when their flights were cancelled due to bad weather.

Authorities called on residents of rural areas to move to shelters due to the risk of flooding.

The NHC said heavy rainfall may trigger flash flooding and mudslides as Pamela tracks into the Mexican states Sinaloa, Durango and Nayarit.

Storm surges are expected to produce "significant" coastal flooding and "large and destructive waves," the center added.

The remnants of Pamela could drench portions of Texas and Oklahoma by late Wednesday and Thursday with the potential for "considerable flash and urban flooding impacts."

Because of its location, Mexico is often hit by tropical storms and hurricanes on both its Pacific and Atlantic coasts.

In August, Hurricane Nora made landfall in the Pacific state of Jalisco, killing a child and leaving one person missing.

Hurricane Grace left at least 11 dead on the eastern coast of Mexico's mainland the same month.

In September, Hurricane Olaf made landfall on the Baja California peninsula, causing minor damage.