SAN JUAN, Puerto Rico — Hurricane Beryl strengthened into what experts called an “extremely dangerous” Category 4 storm as it approached the southeast Caribbean, which began shutting down Sunday amid urgent pleas from government officials for people to take shelter.

The storm was expected to make landfall in the Windward Islands on Monday morning. Hurricane warnings were in effect for Barbados, St. Lucia, Grenada, Tobago and St. Vincent and the Grenadines.

“This is a very dangerous situation,” warned the National Hurricane Center in Miami, which said that Beryl was “forecast to bring life-threatening winds and storm surge.”

Beryl was located about 250 miles southeast of Barbados. It had maximum sustained winds of 130 mph and was moving west-northwest at 18 mph.

A tropical storm warning was in effect for Martinique. A tropical storm watch was issued for Dominica, Trinidad, Haiti’s entire southern coast, and from Punta Palenque in the Dominican Republic west to the border with Haiti.

Beryl is expected to pass just south of Barbados early Monday and then head into the Caribbean Sea as a major hurricane on a path toward Jamaica. It is expected to weaken by midweek, but still remain a hurricane as it heads toward Mexico.

Beryl had strengthened into a Category 3 hurricane on Sunday morning, becoming the first major hurricane east of the Lesser Antilles on record for June, according to Philip Klotzbach, Colorado State University hurricane researcher.