A man is in custody after a security alert aboard a second jet in Detroit

A Nigerian man, in his 30s, has been taken into custody aboard a plane in Detroit after locking himself in the toilet for over an hour.

A law enforcement official said the incident took place on Sunday, aboard the same Northwest flight that was attacked on Christmas Day.

Crew members requested that security remove the man from Flight 253 after he became disruptive.

A Delta spokeswoman says all 256 passengers have been safely taken off the plane.

Delta operates the Northwest flight.

An airport spokesman said: "The pilot requested emergency assistance upon arrival."

Sources told Fox News that the man boarded a plane in Lagos, Nigeria with no baggage.

All 256 passengers on Sunday's flight were taken by bus to the airport terminal for questioning, according to a spokeswoman for Delta Air Lines, which operates Northwest.

Emergency vehicles surrounded the plane as it remained parked about a kilometre from the main airport buildings for more than three hours.

A security official at Detroit airport confirmed later he posed no security risk to the plane. He was a businessman who had become "verbally disruptive" after falling ill during the flight, the officer said.

PA