qgis - Merge multiple linestring features into a single multilinestring

Using QGis or ogr2ogr how do I convert a vector file containing multiple linestrings features into a single multilinestring feature?

At the moment I've been doing this manually by converting the data to GeoJson and editing it manually.

Answer

You can use the Dissolve tool from QGIS:

Vector > Geoprocessing Tools > Dissolve