NetBSD 5.1-amd64 fails to boot in QEMU

[Greg Fefelov <apiocera%gmail.com@localhost>]

Hello.
Recently I've been trying to install NetBSD to my VPS: they use QEMU
(integrated with Xen architecture, I guess) and allow to upload
oneself's hard disk images.
I have had used VirtualBox to prepare the image and it worked well,
but when they have tried to run it, NetBSD kept reloading after
loading the kernel into memory, even before booting process itself.

After that, I ran QEMU on my Windows box with the same result: with
GENERIC kernel it hangs and reboots after
booting hd0a:netbsd
10122216+572416+782784 [727680+477736]=0xd19a68

AMD64 installation .iso anso hangs and reboots after
booting cd0a:netbsd
10122912+5691904+783264=0x10d52a0

..and nothing else. What should I do?