Rap Tour Bus Standoff in OKC -- Cops Suspect Drugs On Board

7:48 AM PT -- Cops have finally obtained a warrant and entered the bus ... and immediately placed several passengers under arrest for "interfering with police process" for locking the cops out of the bus.

We asked cops if 2 Chainz was one of the people on the bus -- to which we were told cops are not sure, but we're told the bus is "connected" to the rapper.

A tour bus connected to Lil Wayne's concert tour has been pulled over in Oklahoma and cops suspect there are drugs on board ... but the passengers have locked themselves inside and REFUSE to cooperate, TMZ has learned.

Law enforcement tells us ... the bus was pulled over around midnight because its taillights were out. And when officers approached the vehicle, they noticed signs of drug use and wanted to board the bus.

But the driver told cops he wasn't letting 'em on ... and locked the door ... and told cops they had to get a search warrant before he would unlock the doors.

It's unclear who's on the bus -- but we're told Wayne and T.I. (also on the tour) had left the city on private jets before the incident. 2 Chainz is also part of the tour -- but no word if he's on the bus.

Cops eventually towed the bus (with the people inside) to a nearby police training facility ... while they wait for a judge to issue a warrant.