  Context. After the detection of a 321-days periodicity in X-rays, HESS
J0632+057 can be robustly considered a new member of the selected group of
gamma-ray binaries. These sources are known to show extended radio structure at
scales of milliarcseconds (mas). Aims. We present the expected extended radio
emission on mas scales from HESS J0632+057. Methods. We observed HESS J0632+057
with the European VLBI Network (EVN) at 1.6 GHz in two epochs: during the
January/February 2011 X-ray outburst and 30 days later. Results. The VLBI image
obtained during the outburst shows a compact ~0.4 mJy radio source, whereas 30
days later the source has faded and appears extended, with a projected size of
~75 AU. The peak of the emission is displaced between runs 21+/-5 AU, which is
bigger than the orbit size. The position of the radio source is compatible with
the Be star MWC 148, which sets the proper motion of the binary system below 3
mas yr^-1 in each coordinate. The brightness temperature of the source is above
2 \times 10^6 K. We compare the multiwavelength properties of HESS J0632+057
with those of the previously known gamma-ray binaries. Conclusions. HESS
J0632+057 displays extended and variable non-thermal radio emission. Its
morphology, size, and displacement at AU scales are similar to those found in
the other gamma-ray binaries, PSR B1259-63, LS 5039 and LS I +61 303,
supporting a similar nature for HESS J0632+057.
