Russia says the trucks contain food, water bottles and generators to be distributed in eastern Ukraine where fierce battles have erupted between the government and pro-Russian rebels seeking independence.
Residents who have been trapped in the crossfire for four months are desperate for aid like this.
But the Ukrainian government is wary. Kiev accuses Russia of supporting and arming the rebels with tanks, missiles and other weapons.
Moscow denies this and dismisses claims the convoy is a pretext to send military supplies to the rebels, who now appear to be on the verge of defeat by Ukrainian forces.
The 260 trucks first rumbled out of Moscow on Tuesday then spent time in the Russian town of Voronezh.
Dozens of them appear to be staying and it is not known if this is the only convoy travelling towards Ukraine.
It is also unclear where this convoy will be allowed to cross the border and whether it will be allowed to travel into the Luhansk region after border checks.
The Ukrainian government may be unwilling to let the convoy cross into its territory, but at the same time it does not want to be seen to be blocking aid.