WASHINGTON — Two airliners were one minute from colliding when at least one of the planes turned away from the other over the Atlantic Ocean this week, federal authorities said today.

The National Transportation Safety Board said it was investigating an incident in which a Delta Air Lines flight and a Russian-registered passenger jet were heading toward each other Thursday north of Puerto Rico when cockpit alarms went off.

The NTSB said the pilot of the Russian plane — a Transaero Boeing 747 — descended 200 feet to 300 feet to avoid Delta Flight 485.

The planes were at the same altitude — 33,000 feet over open ocean — and were “60 seconds apart from occupying the same airspace,” said NTSB spokesman Peter Knudson.

Knudson said the agency doesn’t have enough information yet to know if the planes would have collided had evasive maneuvers not been taken, or if they would have narrowly missed each other.

The two planes were about 180 miles north of San Juan when the near-collision occurred at about 6:30 p.m. EDT. The Delta Boeing 737 — with 152 passengers aboard — was headed from New York’s Kennedy International Airport to Port of Spain, Trinidad.

The NTSB said there were no injuries.

“This was every bit the classic near miss,” said Doug Church, a spokesman for the National Air Traffic Controllers Association.

The Delta pilot told air traffic controllers that the incident was “extremely close” and that he also took evasive maneuvers, said Victor Santore, a vice president of the controllers union. NTSB’s Knudson said he could not confirm the controllers’ account.

There was no FAA radar coverage in the area where the planes nearly collided — as is the case over most open ocean. The NTSB says aircraft are required to remain at least 15 minutes apart when flying through areas with no radar coverage.

Flight plans filed by the two airlines placed the aircraft on intersecting flight paths, which would have been fine as long as they stayed 15 minutes apart, Santore said.

Delta spokeswoman Betsy Talton declined to provide any further details of the incident. “We are fully cooperating with the NTSB,” said Talton.

The NTSB also reported today that it was investigating:

* A near-collision of a commuter jet and a small plane Thursday at Fresno Yosemite International Airport in California. The two aircrafts’ wingtips came within 15 feet of each other during a nighttime landing.

* A small plane that landed Wednesday on a closed runway at Reading Regional Airport-Carl A. Spaatz Field in Reading, Pa.