The Mexican military and high-altitude alpine experts rescued four of five American hikers injured while climbing the tallest volcano in North America, officials said Sunday.

Initial reports said that eight people had gone missing on the country's highest peak, an inactive volcano known as Citlaltepetl, but the figure was later lowered to five.

The Mexican Navy, Puebla state medical services and a Mexican alpine rescue group participated in the search.

A navy helicopter searched for the climbers on Saturday before a ground operation took over on Sunday, as weather took a turn for the worse.

Two of the travelers were rescued by land overnight and were taken to Mexico City, according to civil protection authorities.

Two more climbers were found in the early morning and taken to the town of Tlachichuca before being hospitalized in the state capital of Puebla. They were being treated for bruises.

- Tighter rules planned -

At midday, with bad weather grounding search helicopters, workers on foot were trying to find and bring the fifth member of the expedition off the volcano.

The governments of Puebla and Veracruz states, along with the National Defense Ministry, said they planned to revise rules on access to the peak to prevent inadequately trained or poorly equipped climbers from risking their lives.

Citlaltepetl, on the border of Puebla and Veracruz states, rises 18,372 feet (5,600 meters).

Also known as the Peak of Orizaba, the mountain is popular with climbers but has proved deadly in the past.

On Thursday, the body of a US hiker was recovered from the peak during a risky operation in which a rescuer fell into a ravine and was injured.

In 2015, the mummified remains of two climbers were found at an altitude of 17,000 feet but could not be recovered because of the perilous terrain.