Los Angeles school administrators are urging a union to resume talks as tens of thousands of teachers plan to walk picket lines for a third day.

Striking teachers vowed to take to the streets again on Wednesday despite a forecast for heavy rain across the US city.

There have been no plans for the two sides to re-start negotiations after talks broke down last week.

Los Angeles Teachers Strike
Tens of thousands of teachers have taken to the streets (AP)

Teachers are pressing for higher pay, smaller class sizes and more support staff which school officials say could lead to bankruptcy.

Schools remain open, staffed by substitutes, and the district says attendance is at about one-quarter the usual numbers.