A tally of trucks waiting at the main Terehova border crossing showed more than 600 trucks in line on Wednesday, with waiting times estimated at 73 hours.
A week ago the line was of around 300 trucks.
With temperatures consistently below freezing so far this week, truckers face a miserable and chilly few days.
Other border crossing points showed lines of between 35 and 50 trucks.
Long lines at the Terehova crossing in particular are nothing new, with trucks stacked up sometimes for several kilometers.
The cause is usually an inexplicable go-slow by Russian customs.
LSM's Russian-language service reports Russian media as speculating the build-ups are caused by Russian truckers avoiding Belarus due to import bans on products like meat and dairy. However, later Wednesday Latvia's Traffic Directorate told LETA that on February 27 and 28 Russian computer systems at border crossings experienced technical troubles, now solved.
Adding to the confusion, Latvia's Revenue Service told Latvian Television Wednesday that the lines are caused as demand for western flowers soars on March 8, the International Women's Day.